Hi all new DM here. As the title says this is my first time DMing a real Group. In the past I have practiced DMing on PCs that I made, played, and DMed at the same time to get used to the mechanics. 

This allowed me to get very comfortable with complicated rules, but now I have to simplify it in order to accommodate new players. Any suggestions as to which rules to toss and which ones to keep?

The goal with this is to keep rules that are important and what make D&D unique, and toss the ones that are may be a little less important, or a little over complicated. 

Honestly, you shouldn't need to dump any of the rules. Most groups do handwave away some of the minor mechanics, but which ones are going to vary from group to group, and you can wait to see which ones you find annoying.

If you start at first level, things don't get that complicated that quickly. It all scales up gradually over time.

All that said, I suggest doing milestone leveling instead of XP. It just gets rid of a bunch of irritating bookkeeping.

The only rule that immediatly comes to mind that you might want to simplify is the one concerning spell compoonents. New players get can get confused about when they need a hand free to cast a spell and whether they can use the hand holding there spell focus or component pouch for the somantic component. A simplification I ususally play is that you can do the somantic components of any spell as long as you have a hand which is either emply or holding your spell focus.

Otherthan that just make sure they know the difference betwee na saving throw an ability chaeck and an attack role and they know the features of their character (at level 1 that is quite limited, divine casters technically have a lot of spells to chose between every morning but until they get more experianced they can just prepare the same spells every day and get on fine)

There are quite a few optional rules that complicate the game I would probably say that multiclassing is not allowed for their first campaign, and maybe not allow feats at least early on (not allow the races that give a feat at level 1 and possibly say they must take and ASI at level 4). Other optional rules like encumberance are also best avoided to avoid micro managing but those are less commonly played in general.

The players only really need to know the basic concepts of the game and how there character's features work. As a DM you need to know how all the PCs features work (as well as all the NPC's). You might therefore want to limit the race and class options of the players to what is in the Player's handbook. This prevents a player coming to you and saying the y want to play a Leonin Armorer Artificer with the Quandrix Student background, leaving you to find out what rfeatures they have (and pay for them). If money is tight you can even limit things to the basic rules, there is only one sub class option per class but if noone has player before that sohuldn't be a problem.   

Use whichever rules you're comfortable with, and if you don't know what ruling to make for a situation, make a call on the spot and keep moving forward, because as long as it seems fair to the players, you can look up the actual rule later to use in future situations.  Just make sure the players know if the way something will be ruled is changed from what has already happened.

Most posters here will tell you to keep X, ignore Y, and whatever you do, never ever ever do Z because Z is horrible and bad. But you're new, so I'll give you my advice for new DMs.

My advice is, try to stick to the rules. Once you're familiar with them, you can use homebrew or house rules to fix bugs and improve, but you're learning. Try to figure out what the rules say and mean before changing them.

That said, remember that sorting out every little rules dispute isn't fun. If you get stuck, make a judgement call and move on. Don't be afraid to make mistakes - you can always come back to it later, and your players won't be mad at you. In short, try to follow the rules, but don't let them disrupt the flow of your game.

Finally, remember to take it one step at a time. There's a lot of nuanced stuff in the world of the D&D internet, stuff that tries to convince you endlessly that you're playing wrong. I'll admit that by posting on the D&D beyond forums, I've left my mark on that world of arguments. But you're new. Just focus on figuring out one thing at a time, and be easy on yourself. D&D has a lot for new players to take in, but if you don't stress, you'll find your way.

Don't pick and choose rules, players wanting to develop their understanding of the game are going to reference the rules, and trying to figure out which one's you are and aren't using doesn't actually reduce the amount of effort learning rules.

Play the Rules As Written until you actually recognize the impact of certain rules, some of them might seem trivial until you omit them and see cascading consequences down the line. This is true of even optional rules like Flanking which throw away all the methods of gaining advantage on attacks for a superfluous positioning tactic which will force your players into engaging a single tactic at every opportunity.

What you should worry about is learning and sharing a developed players contract. This will fix 400 times more problems than understanding and teaching the rules. Recognizing the priority of having fun together, cooperating to have fun together, and accepting the necessity of making a judgment and figuring out uncertain rules later ensures that games run smoothly and everyone recognizes the superiority of working together to have fun rather than challenging each other about judgements.

Start at level 1, the game is already diametrically simpler at lower levels where you have dramatically fewer options to choose from. Have a session 0 where you choose or determine a campaign setting and negotiate the character choices everyone makes so they can engage in the setting and with each other. Give the players as much agency over their character creation as you can without letting them ignore the official options and derail the setting. And play a mock battle before you actually start the campaign, maybe a mock social encounter too, that way players can get an idea how their character and party composition perform, and let them switch characters if they find out they made a mistake.

There's more rules and tips than you can possibly retain, so don't try to master everything, having an agreement with the players about cooperating to enjoy the game will fix any mistakes and shortcomings anyone has, your wasting your time trying to master or tailor the experience.

Help the player set up a "go-to" add for their turn. For example, fighters attack with their sword, Wizards cast firebolt, or whatever. The point is, the player should have 1 thing they can pretty much always do on their turn without thinking much.

Then, at the beginning of each session, read through their features and traits with them to help them understand other things they can do.

And don't get wrapped around the axle about whether they are doing the "optimal" thing on their turn. If they ask for help, lay out two suggestions and let them pick. Keep it simple, and let them make their choices.

Good luck!