[RoteLaterne]

I didn't invest a cent and currently play in diamond.

Work the AH and don't buy packs, play tournements for free packs/cards, do the 1927 Yankees in challenge mode and sell cards you don't need for a good price.
Micro manage all of your players, set individual and global strategys, think about batting order, subs, defensive subs.
Set a max pitch count for pitchers you don' trust and avoid high leverage for some guys.
Put in at least one SP into the bullpen and designate him as emergency starter.
Use ballpark factors according to your team. Nothing better than winning a ton at home.
You play 81 games there, design it to your advantage.
Think about L/R splits in your lineup.
Use a leadoff guy with hight contact and speed/stealing.
Think about wOBA and ZR more then e.g. OPS
Train up players for other positions if it improves the team at the end of the day.

There is so much more you can manage to have the maximum output.