It's a good idea to employ an electric razor when shaving your ass. That way, there is less chance of cutting your self in a blind area. Razors with a narrower profile (Braun makes a thin razor) of the cutting head is ideal for getting into the gluttial crevice (butt crack). Use the electric razor first if you plan on also using a disposable razor. Electric razors work best on dry area.

If you're going to use a disposable razore take a long, warm bath beforehand.

Before applying shaving cream, make sure the area is still moist.

Apply shaving cream a few minutes before shaving to soften hairs. Consider using a sensitive product like Coochy Shave or Skintimate.

Be sure to use a sharp blade. You might try usinga brand new blade to avoid irritation.

When shaving, stroke an area no more than twice to reduce skin irritation.

Be sure to clean the area afterwards with soap and water to reducethe risk of infection.

Some people find daily applying baby powder or talcum powder especially helpful after shaving to keep the area dry and irritation free.

Go as long as possible between shavings to reduce skin irritation.

A great alternative is to use a product such as Nair or Neet. Waxing is possible, but you'll likely need an assistant. See my instruction pages for these processes.