Top/bottom dont really matter
Smaller (softer) the cut the faster it will root. If you 'top' your plants then of course you can always root the tips that you remove, don't waste them
If you look at the last post in my thread (today) you can see 2 clones I just cut and placed in my usual home made (cut down milk bottle!!) clone rooter
Its no great science, just keep everything clean and keep the cuts warm and moist. 7 to 10 days you will have roots!
Hope this helps.