First learn the rules, ALL the rules, for the tournament, organization, and local sponsors holding the event. Use them to protect yourself and avoid being taken advantage of off the board.
Never play blitz. Do play faster chess but with minimum time for each move and also a cap on the move TIME that forces you to think first but not dawdle. The old exactly ten seconds per move like the Washington Chess Divan and other clubs used is perfect to be confident if you should get into time trouble.
Clock management. You can NOT afford to just sit and think excessively on A few moves so you get into time trouble. Use the time you need but do not overdo it so that you do not have time you need for other moves. Learn to make a decision. The faster play with fixed max/min per move, not blitz, is a good way to make this second nature.
Think on your opponent's time. You should not need a lot of your time if you do that and then the opponent will be having time trouble and more likely to blunder. If you can get 15 minutes left to 5 in an even position, it is like adding 200 points to your rating.
Learn one opening well. Learn end games well. Learn tactics. The other stuff will come with experience.
For most tournaments you will just play some stranger. You can't prepare for them. If it is a club tournament you should already know the players and there is no need to do more preparation.
Play your game. You have to adjust to whatever type position you have but you have a say in the way the opening goes and the type position that will result in the middle game. Knowing your one opening well will allow you to ensure you get the type position you want in the majority of cases. If you do not like wide open slash and burn tactics you may have to accept that style or else have some prepared defenses that would blunt that approach and give you a game you like. Knowing the typical crap that beginners like shows you the openings you need to also know enough so they don't win early because you made a mistake. E.g. Evans Gambit, Scotch Game, Max Lange, and the like you also need to know cold for black. You will not play those as white.
Your first tournament, when you are ready, should be the biggest and strongest one you can play in. That will maximize your initial rating from which all you later ratings stem from. Play for wins do not give draws willy-nilly because you are afraid of losing. Of course, if you can't win, then a draw is better than a loss.