This is a guide on how to make money on Fifa 12 Ultimate Team.
If you have just started
You can make a few accounts on silver, for example make 3 accounts on silver, just use @mlgpro.com. Then start fifa 12 ultimate team you get given a bronze squad you can discard the whole team which will get you around 300-400 coins each time. It is alot quicker if you have 2 xbox's but if not you just need to sign out and back in on the other account. With The account you want the coins on put up a bronze player write it down then on the siver account with 300-400 coins buy the bronze player. This is one of the best ways to make money as you do not use any contracts or your players cannot get injured etc. Believe it or not this is a really good way to make money but it does get boring. This is a good way to get a decent amount of coins to start of a fairly good gold team.

If you have coins
If you have 50k-1m players are always decreasing in price.
In the day time is where you will find more people on as you probably already know so the best time to sell players would be through the day. The best time to sell players is at night because people will pay more at night as there will be less people up for sale at that time. While your waiting for players to sell/buy just play tournaments your find that's the best way to make money. If you are a decent player and capable of winning online tournaments play them if not just play single player you still get 1-5k.

Formation Cards
Probably the best way to make money.
If you are an experienced Fifa gamer and you have player other Fifa ultimate teams then the best way to make money would be.
Buy for example a Lahm RWB for Bayern Munich with a formation that nobody uses so it will be cheaper. It will be a lot cheaper than buying a Lahm RB 4-4-2 then buy a RWB-RB card and a 4-4-2 card and you can make 5k. You can do this for other players any RWB or RW buy them for as cheap as possible then buy the formation card and the Position card and you can easily make coins. Why your waiting to sell the players just play tournaments.
Good Luck Guys hope this helped.