Once you get into it, it's addictive. It's the best 'card' game/collection among any of the other sports titles. If you are still looking for some tips don't hesitate to PM me, or (speaking for others who've replied) for more information.
Make sure you get some movement with team affinity XP. Some of the team epics are great rewards. Plus you'll get multiple packs while using players from a certain club.
For me, the best way to begin is buying 2 pack bundles. It'll help you fill out your roster. Plus you'll recoup some of the stubs you spent on selling doubles.
There's a bunch of different collections. The started collection can be done pretty quickly... And will boost your XP... FAST. Same goes for the love series collections, and the created player collection. That last one you just go through certain levels of cards, bronze, silver and gold. Those will give you a great boost in XP, which in turn will net you more, better/higher ranked cards.
Just don't let the ratings fool you. Ice been using Blake Treinen since I began, have 86 saves in 91 chances. His base rating is only an 81, but he's usually modded (cards can go up or down in ratings given how they w performed on the actual field). If there's someone you're comfortable with, and are having success with, don't be afraid to stick to it...
The only thing I think they could do better in, is allowing the player to decide how deep he wants his bullpen/bench. If I want to carry 13 pitchers, I should be able to, and vice versa.
When you play ranked seasons, your pitcher will fatigue. So if you rely on someone more so than anyone else, pull him out from your roster for a game and let him get his wind back. Other than that, good luck and enjoy yourself. It's a phenomenal mode.
Sorry I got a little verbose there...