I’ve been DMing and playing in quite a few campaigns with relatively new players (including myself), and I’ve noticed a disappointing lack of role play and character development. Any way to encourage roleplay and/or do it better myself?

A simple one is to give Inspiration to players for creative or interesting roleplay moments. Even players who are just obsessed with the mechanics of the game will be more willing to try out some roleplaying if there's a tangible benefit to it.

Start small. You could start by asking them questions when they roll a skill check. If they succeed on a check and after (or before) you describe the result. Ask how they knew that piece of information or a memory of when they first tried it. When they cast a spell ask them to describe what it looks like. If they kill a creature, what did they do. It doesn't have to be a big fancy description. If they can't that's fine, just move on. You've planted the seed for next time. Look for opportunities to use this information later.

Thank you! I’ll try this as soon as I can. :)

Another big one? As a DM, do character voices, and speak in the first person as NPCs, instead of about them in the third person. It can be a little nerve-wracking for some DMs, not everyone is a voice actor with a huge range, but you don't have to be! I've never seen anyone, DM or player, lean into doing a character voice and had it be received as unwelcome by the others at the table. Players feel more comfortable matching the DMs energy, even if its just jokingly at first, than they are making the first step. And once you're speaking in first person, and in a special voice, it gets less and less likely that you pipe up with side jokes, metagaming comments, "just kidding" chaotic actions that you don't really want to commit to, etc. 

Have characters in the world ask the players questions, and modify their reactions based on the answers.

*An aide is walking the characters to a meeting with the mayor*
Aide: So, <character>, why did you become an adventurer? What's your end goal?
Player: I want to be the best swordsman in the land.

*In front of the mayor*
Aide: Here are the adventurers, m'lord. This one here wants to be the best swordsman in the land.
Mayor: Really? I like someone with ambition. Tell you what, if you do well in this task, I'll allocate some training and sparring time for you with the captain of the guard. How's that?

Or, negative reinforcement:

*An aide is walking the characters to a meeting with the mayor*
Aide: So, <character>, why did you become an adventurer? What's your end goal?
Character: *mumbles* I dunno.

*In front of the mayor*
Aide: Here are the adventurers, m'lord. I have to say, they aren't all that motivated. Maybe you should offer them the less-payng job, instead?

I like to start small. One of my biggest roleplay traits for my half-crazy simic hybrid horizon walker came from when we were at a coffee shop and the rest of the party ordered their drinks and I decided that instead of coffee, my guy liked really weird, gross foods because of the hybridization process weakening his taste buds, and he ordered hot pickle juice. It became a whole thing with that character that whenever he's at liberty to order food the rest of the party is like "oh no, what gross thing is he going to say next?" and we've had a lot of fun with it.

Aside from being funny, it gave me a new avenue to consider different ways that his mutations effect the way he lives and how that impacts his overall motives, attitudes, and goals. And it all started with hot pickle juice.

Try asking your players something small, innocuous sounding probing questions like that, make it sound like you're just satisfying your own curiosity. What kind of food does your character like? What's their favorite type of music? What place that you've traveled to did your character like the best? 

Even if your character doesn't have an answer right away in the moment, it'll get them thinking about that kind of stuff, and soon they'll find themselves thinking in terms of their character rather than as their player. 

By making it fun and being sure they get something minor for it?  You don't need to do voices or silly actions, but you can if you like, just as a DM, try to describe more than just what they see.  Mention sounds, smells, and what they hear.  Rumors can lead them to places they might not have gone otherwise.  Give them things that they do see, but in bright colors or that are beautiful.  There's nothing wrong with any of the suggestions so far, most of them have been great!  Decide what you're comfortable with, and see what happens.

Thanks.

In my honest opinion i would say just be blunt wiht them

Sorry hang on had it all typed out but then lost it all just retyping something now

Be blunt with them.

Tell them your expectations and if they still don't go along with it make them see that your time is being wasted as they are not going along with the roleplaying spirit of dnd.

Maybe turn it into a challenge to entice them via competitive spirit of who can roleplay best, then they might find it enjoyable and do it on their own.

If all else fails, abandon them and play something else (Hate to say this but there's not much else other than), or put up with it.

Sorry if i sound aggressive it's just the way i get my point across, I don't mean to be insulting or degrading of you or any of your party members, though it's disappointing that you don't get to witness full emersion of the game.

Hope my ideas a helpful.

Find in-game ways to play essences with your characters.

If you're not familiar with the game, it's a test of anological reasoning. It's played like this--one person asks question of the group; the group answers, describing someone in the group; the person asking tries to guess who is being described. The question that the asker asks is, "If this person were a ___, what kind of ___ would he or she be?" For example, "if this person were an animal, what animal would he or she be?" The person who is described as "cat-like" is obviously (or sometimes not so obviously) different than the person who is described as "a heron."

In D&D, this could look like, "The bandits search your bags--which, by the way, what kind of bag would this character have?" Or, "describe how your character makes their entrance to the common room." Or, "The guard is asking for the name of your group; how do you answer?"

That's some really good suggestions as well. Looking back at my suggestion i really did come across as a bit forceful or aggressive, sorry.

You can also try short, one-time in-game exercises to nudge players to think about their character beyond mechanics. It's a break and doesn't have to be repetitive. For example:

"It's morning at the inn and breakfast is almost ready. How do each of you start your day?"

"You have a day of downtime in town. How do you spend your time?"

"What do you do to break up the monotony of this tenday of uneventful travel?"

"You're each enjoying a quiet drink in a tavern that's too loud for productive conversation. What do your other party members notice about you for the first time?"

Oh yeah, that makes sense. I really am direct and simple minded lol.

Also that idea and being the haunted one background would work well.

One of the personality traits in the flaws section of the haunted one is that they have certain rituals that they must complete everyday. That could be something to encourage players to roleplay. Be all "What rituals does your character perform and how does he/she/it go about doing them?"

On top of that, just with any personality trait that can be portrayed as such could be a way to initiate roleplaying. For example, if they have a soldier background with the crude humour personality, tell them to describe one of their crude jokes to the other players, which in turn, could trigger an actual legitimate response from the other players, and if not you could ask them how their characters would respond to said joke. Maybe one of the other characters feels insulted by the joke or their personality/morals go against the concept of the joke. How do they react, do they respond calmly or start a tavern brawl or something like that?

I guess when it really comes down to it even the really small stuff like reactions to jokes can make a catalyst for roleplaying...

Also just had another idea!

If some of the players have magic that requires the vocal component, you ask them to create their own kind of chant for when they use that feature like as if they were is some isekai anime or something.

Say they were casting a fire magic that requires vocal components and they could say something like:

"Oh great flame from the depths of hell, come forth and turn my foes to ashes! FIRE BALL!!!"

Probs sound real nerdy right now don't I lol...

Anyway thats just my ideas.

I also thank everyone in this thread as you have all given me ideas for roleplaying with my own groups. Thanks!