Once you have arrived at the location you are going to fish, do a dummy drift to work out the drift direction and speed. In my opinion the ideal speed is around 1 knot as you can cover ground and still be able to fish the area.
Never drive over or drive erratically near where you are about to fish as they are easily spooked and will quickly shut down especially in shallow water.
To get the right weighted Jig head suited to the depth I allow a full cast in front of the drift and by the time it's straight down it should be near the bottom.
Make sure your plastic is rigged straight and as correctly as possible. If rigged incorrectly they will not swim properly or look as natural to the fish and will also not cast as good.
After doing a full cast let it sink naturally as snapper will hit it on the drop a lot of the time. Once near the bottom give the lure a few jigs, release, then repeat.