Basically you should keep 8-9 of your best players plus as many as many 1* players as you have,but because i suppose you don't have many 1* players,start to buy now some 3* players and in 2 seasons,after each level up,they'll became 1* players (also you can sign the 2* academy players and keep them)
When the new season starts,buy 2,3 players for your 1st 11 and 2 or 3 players to have them as subs.
So last day of each season you need to have 8-9 strong players and the rest 1* players to avoid +1 lvl teams ,tanking teams ,some are calling this cheating,but if you like it and don't give a f*** of what others are saying,do it xD
You have more detailed here https://forum.topeleven.com/tutorial...in-cup-26.html from post #242 is updated .