Some information I picked up from Charles Poliquin:

Drop sets for a fast-twitch person

1. perform 4 R.M.
2. drop the weight 10-15% perform as many reps as possible (probably 1-2 R.M.)
3. drop the weight 10-15% perform as many reps as possible (probably 1-2 R.M.)
4. Rest , and repeat for another 2-3 drop sets


Drop sets for a fast-twitch person

1. perform 2 R.M.
2. drop the weight 5-7% perform as many reps as possible (probably only 1)
3. drop the weight 5-7% perform as many reps as possible (probably only 1)
4. drop the weight 5-7% perform as many reps as possible (probably only 1)
5. Rest , and repeat for another 3-4 drop sets


Drop sets for a normal fiber type distribution type

1. perform 8 R.M.
2. drop the weight 5-10% perform as many reps as possible (probably 3-4 R.M.)
3. drop the weight 5-10% perform as many reps as possible (probably 3-4 R.M.)
4. Rest , and repeat for another 2-3 drop sets


Drop sets for a normal fiber type distribution type

1. perform 6 R.M.
2. drop the weight 20% perform as many reps as possible (probably 12)
3. drop the weight 20-25% perform as many reps as possible (probably 25)
4. Rest , and repeat for another 1-2 drop sets


I personally tried drop-sets in 6 intervals, where I drop 20% each succeeding set and goto failure each time. Very intense if you are looking to change things up.