Astigmatism simply means that your eyes are steeper in one direction than in another. Think of a football (American football). An eye with no astigmatism is shaped more like a basketball. LASIK treats astigmatism very easily. Generally, the preparation is the same as for ordinary LASIK.
General preperations include staying out of contact lenses for 1 week or longer depending on the type of contact lens and the length of use. Depending on the recommendation of your surgeon you may take some eye drops a day or two prior to LASIK.
However, other than that there's not much to do other than show up!