Basically here's my advice:
First of all, the standard starting players are unsustainable. Despite being low/fixed value, their wage cost is overinflated due to a substantial amount of teams owning these players. Start out not buying anyone, and run out the existing contracts of these players and sell them when they expire. All of them.
Importantly, don't release any players who already have an existing contract. These players are bought and payed for for x amount of matches and releasing them is uneconomical.
There are many players who have equal/better overall/stats than the starting players and are cheap. More importantly, their contracts are a lot cheaper that the starting players. Look hard and you will find them.
Always put players on 50 match contracts if possible as it is far more cost effective/economical in the long run.
Look out for players early on who have multiple positions but get a better rating and/or are more suited to one of their other registered positions. For example, Odemwingie has 68ovr for CF. Move him to RMF/LMF and he gets 78ovr. Rooney goes from 90ovr CF to 95ovr RMF. Occasionally you can get a very good bargain this way.
Eventually build a squad, not just a team and try to find a balance of player form arrows/synergy. This may become a constant work in progress.
Don't buy too many players in a short space of time as the standard 10 match contracts the players come with can hurt you if you're not careful.
Try not to buy any players when their form graph is declining. For instance, if you buy a player with a green arrow and a standard 20 day graph on his last day of green, he will be blue for 2 days, purple for 4 days and blue for another 2 days before going back up to green.
Obviously stamina can be very important, once a players stamina depletes to 50% during a match, his stats start to decline for the rest of the match. Also the less stamina the player has the likelihood is that he'll take longer to recover fitness and therefore be unavailable more often than a player with higher stamina.
Basically, that's the basics. Once you are a few hundred games in, you can think about synergy and dream teams etc
PS. If you happen to play a 4-5-1 with long ball, buy Miruic. He is a monster. 700+ matches in and assets of 400 Mil, Miruic is still part of my squad
