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!
Stop contacts. Start artificial tears. Stop caffeine n alcohol. Start drinking more water. Bring in all your old rxs so your surgeon can assess your myopic progression and extrapolate and overcorrect so you won't need an enhancement. Many centers ignore the last part so have bad enhancement rates
Many primary eye care providers still think that LASIK cannot correct for astigmatism so we still have patients who have been told that they thought they couldn't have LASIK because of astigmatism. Only the first generation of laser could not correct for astigmatism. It has been more than a decade since lasers could successfully treat astigmatism.
Since people with astigmatism often wear toric soft or RGP contact lenses, they will generally need to be out of contact lenses for longer than a person who wears spherical soft lenses. Toric soft lenses and RGP lenses can reshape the cornea slightly by pressing on different parts of it during wear. We often recommend patients to be out of contact lenses for a month or longer if they are wearing contact lenses for astigmatism.
Except for this, preparation is generally the same as for people without astigmatism. The calculations for the laser treatment and specifics of the type of surgery might change but these generally don't require any changes be made by the patient in preparation.