From my experience, I will be talking about transfers.
Forms
First, look at player's quality, not just their stars. Stars visually drop by 1 as you got promoted, but his skill doesn't decrease. Hover at stars to see players' quality, the player which is close to getting 1 more star will be the most efficient.
Second, be sure to check their forms, as high-quality players may mess up with your team and make your team's performance drops.
Third, check out their ages. 3* players with low ages can be a very great way to train them and become your long-term resource. Or if you are currently struggling, a very old 5* players that is very close to next star may be your another great choice if you're struggling for a lead, a CL spot, or a promotion spot.
Bidding Wars
-Bidding wars aganist noobs may be tough, as they will always try to go for a lead, such as when he is outbidded, he will immediately response by placing another bid, and keep doing so, or even placing multiple bids in the same round to get his current $ price goes up. This may be annoying, but they will continue to waste their tokens and gone out of power.
-If your internet connection speed is no good, you may try to bid at the beginning of the new round, as you will stands a chance of getting a player if all players involved ran out of tokens. If your speed is fast enough, bidding at the end of the round will be better.
-Think about time zones, as more players in the east playing T11. Think about bidding styles of player from each country, such as Thai players will bid from 10:00 GMT (17:00 GMT+7) to 17:00 GMT (0:00 GMT+7), try bidding from 11:00 GMT+7 to 12:30 GMT+7, but watch out for Asian bidders, as they are completely annoyed.
This may helps. Thanks.