The first trick I use is a double-rig (also known as a fish-finder rig). It evolved from commercial longliners in their search for Bluefin Tuna. Scaled down, it is a very efficient rig for crappie. Simply rig two # 4 Aberdeen hooks on 6 dropper loops, about 3 apart, over a 1/8 oz. bell sinker, or several split shots. You can fish this under a slip bobber, or anywhere from the bottom up tight-lining (or vertical fishing, as it is sometimes called). You can also omit the sinker and hooks and use two 1/16 oz. marabou jigs under a slip bobber. This is deadly for crappie in heavy cover. It is not uncommon to hook two crappie at a time with one of these rigs. I usually tie a white or yellow jig on above a chartreuse jig. Another trick is to omit the bobber, and tie a small crank-bait on under the jig. It gives the appearance of a small minnow chasing an even smaller one, an irresistible situation for any predator fish.
When minnow fishing slows down, try this trick. Take 6 or 7 minnows and place them in a 2 qt. or gal. glass jar with water in it. Punch a few small hole in the top to let water and smell circulate. Then tie it with a small rope so you can lower it into the water a few feet. Now fish near the jar. The crappie can smell the minnows and see them, thinking it is a school of unwary baitfish.
In winter, when crappies are hitting very light, you can make a strike indicator out of an old guitar low string. Simply tie on a 4 length of the guitar string onto the last section of your rod, with the ball-end even with the tip. Then bend the string up and away from the tip at a 45 degree angle. Run your line through the ball-end of the E string, then through the tip guide of your rod. You can now detect even the lightest of hits.
When hooking minnows, you want them to be able to swim, so it is best to hook them through the eyes, jaw or just behind the dorsal fin. Be careful not to stick the lateral line, as this will instantly kill the minnow.
Another one of may favorite tricks that works around 90% of the time when crappie get lock-jaw is to rig a bobber, a spilt shot and #4 Aberdeen hook. Then, take a 1" to 1-1/2" minnow and hook it through the lips.Take a pair of fingernail clippers and clip a small portion of the minnow's upper or lower tail fin. Not a very big piece, just a very small nick. This causes the minnow to swim erratically because his tail fin is now unbalanced. Cast this rig into likely places and let it sit. Now, take another rod rigged with a small crank-bait and cast it past the bobber on the other rod, and reel it past the rig continually. To the crappie, this appears as if a smaller fish is going for your bait and is inattentive to his surroundings.