Kids are have a better chance to improve at chess compared to to adult players. There are many reasons behind this but the most natural reason is that kids have a lot of time at their disposal compared to most adults, who have a limited amount of time because of their responsibilities. So what you’re doing during your limited time is vital.
So what should you focus on, the opening, middle game, endgame, tactics, positional play or strategy? Perhaps the best is to study masters’ games which serves all purposes. Here the key question is which games should be studied, and the best way to decide this is to find a coach who can analyse your games and define your playing style. Based on that you can choose a player and study his games. For example when I started taking lessons from Nigel I told him that I liked Garry Kasparov, but he advised me that my role model should be someone else as my strengths and weaknesses made Kasparov unsuitable. Afterwards I started to study Capablanca’s and Geller’s games, and the results have been quite positive for me. Another thing you should do is to select games which have been annotated by the player himself.
Another major benefit of game study is that it gives you a feel for position, a kind of intuition about what should be played. For example in this game it is easy to calculate out Qe2 and Nb5but the problem is in finding these moves in the first place:
So if you study these sorts of games you will find similar kinds of moves in such positions. Moreover it will become your second nature if you do it seriously.