I'll give you a few tips. If you just want to change a couple of players on your team, do it before you start franchise mode. Goto my madden, then nfl rosters. Then make some trades. The trades will almost always be agreed to. Then after making the roster changes, save it. Now start your franchise game. Your franchise mode roster will reflect the changes you made before. This way I added Calvin Johnson and Suh to my team. Yeah, try running on wilfork and suh! And Johnson is just a beast.
As for the draft, you really should pick your own players. If you go through the scouting process, you can narrow down the better players. When you bring them in for personal workout you will get letter grades for their potential. The A ones are obviously the best, make sure to draft these players. and sometimes A rated players are not even 1st round graded, so just draft them 1 round ahead of where they are graded and you guarantee you will get them. That's called getting a draft bargain!
Last of all, your picks are considered very valuable by the CPU before the season ends. So after 4 games into the franchise season, check out the standings, then trade your picks to the worst team in the NFL. For example I traded my 2011 1st round pick to say the Dolphins for their 2011 1st round pick, and their 2012 1st round pick and 2012 2nd round pick. That's right, the computer really undervalues future picks, so if you're willing to defer your reward, like BB does, you can really stock up on high future picks too! This should be enough to allow you to dominate the draft. In the first year I acquired the #1 overall pick in the draft while having like 4 first rounders waiting to be used in the next draft. Now with a #1 overall pick, you can trade for just about any player that you want, and of course get in return that player plus future picks.