I do 300 quality jelqs, with my left hand only, and my right hand over my left for added pressure, it takes about an hour a day.
I usually do 50 reps, and sit down, and stretch a bit and slap my dick on my thighs and think of something good, and erection comes back.
If you really can't get an erection, you're either doing it too hard, or you're doing it downwards. Upwards = harder erection and thicker, Straight = longer, thicker, not as thick as upwards tho. I like a medium upwards.. you can tell this by standing in a mirror sideways while jeqling.