You need to study the basics. Chess is a very complicated game but lots of work have been put into breaking down each every facet that you can study every possible combinations that have ever been played. You can find some great books offering clear analysis and explanations regarding the phases of the game. For example, the Irving Chernev’s classic Logical Chess and Laszlo Polgar’s Chess: 5334 Problems, Combinations and Games. Read them and learn from them.
And don’t forget to practice what you have learned regularly. Play every chance you get. Only then you can test if you are applying what you have learned so far. It’s good that you are joining local tournaments because that will pit you against players who might be better than you.