I used a bit of information from other posts here. My profs are aware of my law school interest. I just told them I will be applying this fall and asked if they would. I offered to go to their office to talk if they wanted to. I'd offer a transcript, resume, and anything else you'd think would help them write the best letter possible. Both just said to give them an unofficial transcript, resume and any other relevant info, like a PS, Since you know them well, just let them know how you're doing, working and such, then go straight into applying for school and ask.