Many will simply tell you to push up or down on the right stick... But that's a short sighted view of shedding blocks. While it will work to get you off a block, you will need to master other facets of playing while engaged if you want these moves to work effectively...
I control all 11 players on defense, but my favorites are DT, MLB, or a safety. Because I play in the middle alot, staying clean and shedding blocks are priorities.
1) Just because you're blocked, doesn't mean you can't still make the play.
Sometimes it's beneficial to stay engaged and push your opponent into the backfield. Learn how to use the SPRINT button to push the player blocking you. Sometimes maintaining your contact is your best bet to stopping a play.
2) Combine moves
I find pumping the SPRINT works best in conjunction with right stick moves. Engage - Sprint to push - Right stick left/right to gain separation - Sprint to the target to maintain separation.
3) Master the Toss & Tackle
When you're playing at the point of attack, sometimes you want to stay blocked until it's time to make the play. To get the most out of a power move, Press Sprint as you engage the blocker. Pump it to maintain control of the blocker, then as the ball carrier approaches make one last Sprint pump and combine it with a power move to toss the blocker away to the off side and make the tackle.
Although the power/finesse move may get you loose for a moment, if its not followed by another move immediately, there's a good chance you'll have to fight off the same blocker again.
Hopefully you can use this to get better results...
Later