Your best 14 players are taken into account for match making.
So identify your best 7, 8 players and invest your greens in them. Make them mutants and keep them in your team permanently.
Near season end sell all your other player and buy 3 star young players ( preferably who have no SA and and who can play only 1 position ) so that they can be in your team for a long period of time. Never train them. Only train when you have to get your training bonus to 10. Make them learn new positions and SA this way their quality won't increase for many seasons.
Now if you want to manipulate on extreme level you should also release your Youth Academy players as they would be counted in match making because except your 7, 8 players their quality will be higher than the 3 stars players you bought.
When new season beings just buy few players who are just above 80 percent quality for 1T. Use them for the whole season and again sell them on the last day of the season.