There are some players that boost an attribute of all other players. Flashback, Draft and Game Changers will affect ALL other players in your lineup. For example, if you have a Draft CB with +1 AWR, it will boost the AWR of ALL other players in your active lineup. Game Changers give a +2 boost but also have a -1 for another attribute. If someone has completed the Domination event and earned Domination Richard Sherman that will add +5 AWR to ALL players. The boosts stack, so you can have 2 +1 AWRs for a total +2 AWR but you cannot boost an attribute above 99.
Captains and MVP players will boost only the players on the same real life NFL team (as they were at the beginning of last season). So if you have MVP Jay Cutlet he will boost all other Chicago Bears only.
If you go to this site, http://forum.ea.com/eaforum/posts/list/10332648.page#34905652, it gives you an idea of which boosts are better than others. Awareness (AWR) is the best. It also links to an EA spreadsheet that shows you how each of the attributes contributes to OVR for each position
If you are looking for general advice on the game I would recommend the EA Madden Mobile Forum (http://forum.ea.com/eaforum/forums/show/3936.page) or MUTHead (http://www.muthead.com/forums/madden-nfl-mobile)
