Usually when the water temperature hits the upper 50's to lower 60's the Crappies will start to move into shallow bays, coves, backwaters, etc. where the water tends to heat up quicker than the main lake. The peak of the spawn is typically when the water temperature reaches 68-72 degrees.
There are a lot of ways to target these fish when they are up shallow but my 2 go-to techniques are with a small moving bait to cover ground and find fish and then when I do I usually present a Maribou or Feather jig suspended under a Bobber or Float. My moving bait of choice is usually a 1/16th oz. Spin'r Grub by Johnson and the jig I like to use under a Bobber is a Kenders Tungsten Feather or Maribou jig. I prefer Tungsten as it can get down to the fish fast, allows for long casts and it eliminates the need for a sinker (which always seems to tangle up my line). You can also remove the bobber, cast the Tungsten jig out on its own and "hop" it back to you to trigger bites and cover water.
This is a good reminder that all fish during the spawn are usually at their most vulnerable and easiest to catch. It's important to practice Selective Harvest (or Catch & Release) as over fishing a lake or area can really hurt a lake's future population and size dynamics (ie. removing Males while on their nests or defending their fry will ensure that the eggs or fry have a high mortality rate).
Here is a short video from a recent outing where I used the techniques mentioned above to find a school of Prespawn Female Crappies: