First priority is to only bid for the players you need the most. So work out exactly what players you ideally want in your squad. First priority is then to get players who can play those positions.

Second priority is to get good (4* or 5*) players for those positions. Old players are cheap and there's usually not as much competition for them, so I'd suggest these.

Third priority is to get good young players for those positions. Young players are expensive and in high demand. It's probably not worth even trying to buy them until you find out a quiet time on your server. The first 2x priorities should keep you buy for a season or two anyway, so you probably won't need to focus on young players for a while yet.

For myself, I have an excel spreadsheet with the positions I need to makeup my ideal squad. I then colour code it red/yellow/green, depending on whether buying them is a 1st/2nd/3rd priority.

Also when bidding, to conserve tokens here are a few tips which I found useful:

1/ Wait until the last 5s of the auction before you bid. If someone else has already bid on the player, don't bid. As you don't want to get into a bidding war.

2/ If someone else bids after you do, try to win the player. BUT, look at the person you're bidding against, and see if they're a token buyer. Easiest way is to look at the value of their team compared to their level. Also token buyers usually have premium logos. If they're a token buyer / video watcher, then it's probably not worth bidding against them.

3/ If you are bidding against someone, bid early in the first knockout round. They'll then bid over you. In the second knockout round, they likely won't bid until you do (Since they're already winning and don't want to waste tokens). Wait until the last 2-3s and then place your bid, thus not giving them enough time to bid after you.

4/ As you already know, find a quiet time on your server. To find the best time, look at the times when games are usually scheduled. These are the worst times to look for players, as everyone is online watching/waiting for their games. While they're waiting, they'll buy players. On my server, around 2-5 hours after the server resets to a new day is often a good time, as there are never games scheduled then, and it's really late in Europe. Also don't even bother looking for players in the weekend, there will be wayyyy too many people online.