Just experience, if you haven't done anything with it before then you could look at some courses, I haven't done one myself but I'm sure kamco may offer training courses. And as Riley said, get insurance.
As for drains, unless you want to go into commercial then a set of rods and some gauntlets should be all you need. Just learn about different systems so you don't end up charging a customer for works they could get free from the local authority.