To become a good solid 2nd row you need to have the set peice down as your basics and then work on your open play work.
So get your Scrum, lineout, kickoffs top notch and then look and expanding your game.
In defensive open play you want to stay near the ruck, looking to drive the opposition back in the tackle.
On offensive play you either want to be support the player with the ball or taking the ball off the 10 (0r 9 if your team plays like that).
The thing to remember is as a lock don't look to hit everything, you need to make sure that when you do somthing you give it 100% of your energy so don't act like a flanker hitting every ruck. I try and hit every other ruck, or if you have just carried the ball, next phase be a supporting player.
Hope that helps.