Sal;
Take a look at Gandolf’s video of jelking. Do it that way and you can’t go wrong. Lots of lube is important.
I have never had the slightest damage from jelks and it is, imo, one of the best exercises for length and girth that you can use between pump sessions. Just build up on them slowly. Start with 30 or 50, see how you feel. Add about 10 more strokes each PE session. You’ll be up to 100 in no time, then 300, then? up to you and your dick.
I also like flaccid stretches, all directions, right after the warm wrap and before a pump session. This loosens up the tissues, the ligs and prepares you for jelking to follow.