A BIC is the first step for both. For AFF you'll need 360 minutes of freefall, and your proficiency card filled out before the course starts. There is a lot of work to do in filling the cards requirements. I recommend getting the card even if you don't have the FF time yet. That way you can focus your remaining time needed on your required jumps to fill it. An AFF card not only requires you to fly like a madman, but also teach pre and post jump materials. Tandem is a lot easier to get qualified for and will keep you busy. After a BIC, 500 jumps, 3 years in sport-"time sense your 1st jump," and tandem camp, then your 5 level 2 jumps your making money. I used my tandem income to pay for my AFF training and JCC's. Yes, I said JCC's, it took me more than 1 camp to get it right. Be prepared to leave your ego at the door when you go to AFF camp. Even the hottest skydiver can have a hard time at AFF camp. Train for AFF flying, there is no other type of flying to prepare you but focused AFF training dives. Most of all you have to love the sport, because that is what you will be personally representing as an instructor. Have fun!
Before you attend the AFF Certification Course, get lots of instuctional and coaching experience. Get to the point where teaching from a lesson plan and remembering junior jumper's freefall gyrations is second nature before you get anywhere near an AFF Evaluator. For comparison, to become a Canadian Progressive Freefall Instructor, you must have the 6 hours of freefall time, plus Coach 1, Coach 2 and Instructor A ratings. As a coach, you develop all those proximity, observation and analysis skills that are second nature to freefall instructors. The nearest American equivalent would be Skydive University coach certification, but then Skydive U. is headed by Rob Laidlaw. Rob led the Canadian 4-way team to how many world championships?
By comparison, tandem instructor ratings are much easier to obtain and the job pays better. Aside from the usual 500 jumps, 3 years in the sport, 1 cutaway and some sort of instructor rating, you need a calm demeanor and and a strong back. The calm demeanor will solve half your students' stability problems before you ever get near the door. The strong back is required for lifting those 45 pound rigs and reluctant students. In the long run, you will find it easiest to tell students "just put your feet on the step, your arms on your chest and let me do the rest."