Which technique should I use if I’m trying to catch Crappies in areas that have a lot of rocks?

Generally Crappie choose not to hang around rocks but if the rocks have lots of plant life on them where the bait fish can feed the crappie will follow.  Start by fishing the rocks when the waters are coolest.  After that there are many techniques that will help you out.  First and foremost you really need to know the layout of the rocks and surface under the water.  The goals is twofold: catch the fish and recover your bait or lure.

One of my favorite tricks is figure out the depth of the furthest point that I can cast (assuming a natural smooth grade), I will then place a bobber at that depth then as I pull my rig closer to the bank I will pull it faster keeping the rig just above the rocks.  This technique also works well when you might be trolling for fish, a heavy jig might go a little lower but a shorter line from the bobber  should keep it off the rocks.  If you are really good you can match your speed to the overall surface of the rocks.  You can apply all sorts of physics here but gut feeling and trial and error will be your best friend.

The best option for fishing the rock, if you can, is to fish the edge of the rocks.  Big rocks do not tend be a good option for spawning and most of the time they do not provide lots of shelter but they provide warmth and oxygenate the water that the small bait fish love just expect your target to move fast.