Here is a list of skills that are essential to be good in TFT. Each of these contribute to winning a game, but are not weighted equally. The more of these you master and consistently apply, the better you will be at TFT, which will affect your ELO and rank. If you do not know what to improve on, take a look at this list and pick out one skill at a time to truly master.
More guides to elaborate on each of these skills to come!
Economy Management: https://youtu.be/uCOBkRDk308
Team Strength Assessment
Reading the Lobby
Game Mechanic Abuse
Composition Matchup Knowledge