I just started playing this as well a few weeks ago and this is what I did and right now I have about 250,000 coins and some great cards. Play games to earn some coins then buy the gold packs. Start a collection from cards you get in the gold packs then put the cards you don't need up for action set the buy out price for what the cards worth and set the time for an hour and it should sell. What i did is try to finish the college collections first some of the easy ones are college collection like Ok. state collection is only 5 cards and u get a K. Williams card and 50,000 coins in return. Get two players from that collection then if you have 30,000 coins buy the rest from the auctions you net 20,000 coins doing so. Also the Jersey and stadium collections are easy. If you need any more tips hit up youtube and watch some videos and here a great site to help find out what players to the what collection http://maddenultimate.com
Hope this helps its kindof long post but these tips helped me get a good team and lots of coins. Skol Vikings.