the fastest way to improve your game. it is to watch strategic videos and to be inspired by them for your game. I advise you to play several hundred hands per day to acquire experience and automatisms. which will be very useful to you on MTT and will allow you not to be too tired when you reach a final table. when you lose in a game. try to analyze the spots where you lost your chips. if it is because of an error on your part and not of the variance. you have to solve the problem and no longer commit it in your next games. it is thanks to this technique that you succeed in advancing and improving your game. I hope that these tips will be useful to you and I wish you good luck with your next games.
It is really up to you to identify the weaknesses in your game; without a lot of specifics, it would be impossible to us to identify leaks.
Assuming that you are fairly new to poker, but have a fundamental understanding of how the game works, I would suggest searching for Evan Jarvis' Triple Threat YouTube videos; they are a great way to introduce you to basic poker strategy and he keeps it straightforward and easy to understand.
"Success is not final, failure is not fatal: it is the courage to continue that counts." - Winston Churchill
You need to be able to watch your opponents and their style of playing (how they bet when strong/weak etc.) And have patience. Also being more specific about your troubles in game will help us to help you identify and improve your skills.