It's been a while since I've posted here, but I'm trying my hand at being a DM in this homebrew campaign that revolves around deities and conquest. I usually fall off as a DM due to my lack of improvisation/stuttering, which may ruin the immersion for my players (which are mostly family but yeah). Though, it should be said, that I am fairly new to DM'ing in general, and I think I understand the basics done after watching every video I could. On paper, I'm a great writer/author and I love to use descriptive words to describe sceneries and characters; but I just can't seem to bring it all to life. Tips/advice please?

Make them describe stuff.  When they walk into a tavern, instead of describing it to them ask them for details about it.

When someone asks "what do I see", ask "IS there anything in particular you're looking for?". That one's saved my bacon a couple of times, when I've forgotten something or missed an obvious feature. One character found the deeds to his ancestral home in a safe because he reminded me that they might exist in this way - otherwise it was just going to be documents and ledgers on the mine!

Involve them in the description. Instead of detailing it all for them to listen, engage each of them - "Grog, from your high perspective, you can see the top of the bar is covered in etched graffiti of names. Bernie, from so close to the ground, you notice that the table legs in one corner are chewed, as though by a dog." That sort of thing is helpful to snap players back to attention when you're describing.

Remember to convey what your characters may feel or perceive from place, people and ambiances, describing in various details what they see, hear, smell, taste, touch, what their intuition or gut feeling tells them. Asking your players questions is a direct way to keep them engaged, not just what they do, but what they think, how they feel like or how they see a given situation. Asking them to be more descriptive in their action and motive is also a great way to make them more engaged. Appointing one of them as the chronicler taking notes of the campaign story can also help, having another keep track of party treasure, watch tour and walking order also help.

Also worth checking their classes for those abilities they might neglect to mention like the Paladins ability to detect good and evil passively. That came up in my game without me expecting it, and now I am aware of the goodness/evilness of the world around them for my descriptions. Also directly involves them: "You, Dogood Holymann, get a sense of peacefulness and light from this place, despite it being so dark and long neglected. The air here smells fresher."

Doesn't outright tell them it's good but if they remember why their character might sense this, it will do the job!

Have you asked your players for feedback? I find that sometimes DMs are much harder on themselves than they need to be. What you believe is boring or ruining immersion may actually be very engaging to your players, only they aren't vocalizing it. 

I'd recommend checking in with your players about it. "Hey, just wanted to see how you're liking the game. Is there anything you'd like to see more of?" See what they say. If they're newer to the game, they might not have opinions, and it's okay to prompt them by saying stuff like, "Do you feel the setting comes alive? Does the way I narrate spark your mind's eye, or interest you?" You may come to find that they don't really care about descriptions, or that they think you're doing a fantastic job already. 

Yes, and they agreed about that I'm not the best at immersion. Although they seemed pretty fine with it, I really do want them to enjoy a good session where they're focused and not constantly asking for what I last said! Idk, it's more what I strive to achieve then them; but last session, they said it right after we ended off.

Quote from Plaguescarred >>

Remember to convey what your characters may feel or perceive from place, people and ambiances, describing in various details what they see, hear, smell, taste, touch, what their intuition or gut feeling tells them. Asking your players questions is a direct way to keep them engaged, not just what they do, but what they think, how they feel like or how they see a given situation. Asking them to be more descriptive in their action and motive is also a great way to make them more engaged. Appointing one of them as the chronicler taking notes of the campaign story can also help, having another keep track of party treasure, watch tour and walking order also help.

 That's pretty good advice, considering all in my group are new to this. I've also tried to ask one of them to be the chronicler, but no one really wants to.

Quote from ThorukDuckSlayer >>

When someone asks "what do I see", ask "IS there anything in particular you're looking for?". That one's saved my bacon a couple of times, when I've forgotten something or missed an obvious feature. One character found the deeds to his ancestral home in a safe because he reminded me that they might exist in this way - otherwise it was just going to be documents and ledgers on the mine!

Involve them in the description. Instead of detailing it all for them to listen, engage each of them - "Grog, from your high perspective, you can see the top of the bar is covered in etched graffiti of names. Bernie, from so close to the ground, you notice that the table legs in one corner are chewed, as though by a dog." That sort of thing is helpful to snap players back to attention when you're describing.

 Noted for next time!

Quote from Lunali >>

Make them describe stuff.  When they walk into a tavern, instead of describing it to them ask them for details about it.

 Interestingly, this is where I have to improvise the most with their rickety, quite-odd descriptions.

So there's this RPG called Kids on Bikes.  And part of the primary conceit of the game is that once the Story Teller gets the game going, they can back off and let the players "just play".  When you think about it, most people know what a reasonable DC is for a given check.  "Is this hard?  DC 15".  But bigger picture the players create a lot of the world as they go.  If you're not comfortable with the improv, and your table is cool with sharing the work, there's nothing stopping everyone from contributing and building the scene out.  You know, maybe, that the shady guy in the corner has a job for the party.  Cool.  That detail is locked in. 

But the barmaid?  Let someone else describe her, or even RP as her for a bit.  What kind of food is cooking?  Hand that off to the table-foodie.  Leadership is delegation my friend.

There's been a lot of advice on how to involve players in narration, and I think it's a good tactic if you have players willing and comfortable with participating like this. Ultimately, though, they expect immersion and storycrafting leadership from the DM. 

Some techniques that might help you:

- Create unique/unusual elements in your worldbuilding. Maybe grass changes color based on the weather. Maybe the locals worship a stuffed ferret named Bob. Maybe coin was outlawed and everybody pays with elaborate compliments. If you create cultures, details, or quirks in your world that catch your players' curiosity, imagination, or humor, you can dramatically improve immersion.

- Pull backstory into the foreground. If your players are open to it, use parts of their backstory or character design to flesh out your world via NPCs, locations, customs, stakes, or mysteries. Players tend to get more engaged when things affect their characters directly. 

- Describe scenes for all 7 senses. Yes, 7. This is D&D land, where spells exist, so the six senses are touch, taste, sight, sound, smell, and magic - and a seventh I like to include on occasion is emotion. You don't have to include details for every single one of these in all of your narration, but sprinkling in comments about how the wizard is aware of an unsettling arcane pulsing in the air, or the ranger catches a whiff of rare wildflowers on the wind, or the monk senses a ripple of fear in the otherwise tranquil town...that can make the setting come alive and include the PCs in the experience at the same time.

- Give the people what they want. I alluded to this in my question post, but if your players are struggling with immersion, it might be in part how you describe things, but it also may be the content you're focusing on. Some players don't care about the scene descriptions and just want to chat with NPCs. Others just wanna kill some baddies and get loot. Still others really need to have a location described to the minutest detail so they can picture it. Players might be bored because their favorite part of the game isn't coming up as often as they'd like. Do your players pay attention in combat and zone out during RP? They might be hack'n'slashers, and it's okay to focus more on describing how they're kicking butt in combat. 

There are other things you can try too, but these might be a good starting place. Know also that you will get better at this with time, so be patient with yourself as you learn what your table needs. 

A few ideas.  One, rehearse.  I have taught professionally quite a bit and I never gave a lecture without being very familiar with my notes and the subject.  I talk through key scenes at least three times before we play.  I try not to write this out, but I have a few key points I want to emphasize and I craft my soliloquy around that.  You don't want to forget about the sconce on the wall because that triggers the secret door but you don't want to overemphasize it either!  But don't misunderstand me, it is not long talk.  No one wants to sit through a thirty minute description of a room with no combat, secret doors, etc.  But rehearsing a few key sentences allows you to "press play" when they set off a trap, come upon an unusual room, etc.   

Two, I have a typed up sheet of words to describe sight, sound and smell.  They are organized by general words (e.g. faint odor, overpowers your nostrils, pungent) and positive (piquant) and negative (foul, rotting).  I found describing anything but sight was difficult for me and even with sight I stuck to only a few words.  I have something similar for NPCs; a list of names, facial features, body types, etc.  Now I have a few dozen words for each sensation on my screen and it makes me less likely to fumble for words when describing things or when I need an instant NPC.  Lastly, I have a similar sheet for combat with a column of body parts and a column of action words.  Mix and match and you get a ton of options for combat narration at your fingertips. This is much better than, "He hits.  You miss.  He hits."  

These lists of words are especially helpful as your players go off the reservation and you are stuck improvising because they went into the forest instead of the cave.  Happy to share the file if you want it.  

I also try to make the players do some of the work as others suggest.  What do you see?  Where do you think this goes?  You get a critical hit!  What happens?