Hi bud, start looking to up grade your weaker players and I find a good time to buy new ones is in thelast weak as higher level players are of loading there weaker players!, heres the thing, there weaker players are a star higher to you so are good for you!, try to get 5* that are 3/4 or 8/9s this way when you go up a level and he loses his star he is not far off getting it back.
Dont try to buy in the first week or so of the new season as players will be expensive and many many bidding wars occur as managers go on a frenzie to better thier teams, look for young and hot prospects.