Also,
you want to move your thumb and pointer finger in the OK sign from your shaft to your glans. If you can do so without moving your whole hand or if you need to move your whole hand, arm, etc. What's important is moving that "ring" all the way down your penis until you get to your head while watching you head expand, get red, and get big from getting filled up with blood.
Since I am cut, I wouldn't know how it is for those that are uncut. I would assume with the hand that is not doing the jelqing motion you should pull back on your skin and keep it at your base while you do your jelq with your other hand. You can also switch hands from time to time. I am cut and sometimes I put my other hand at the base just to get my penis tight and perform a real effective jelq. As far as losing erections, well your erection level at 25-35 percent would be optimal for length gains. If you want girth then you should stimulate before and during your jelq sessions as needed. You should also try Kinpole's erection tea, you can search for it here and it's easy to make. Lots of people are drinking it and getting good results.