As dickerschwanz has said, you want to start with light pressure. The reason is to get a more personal feel as to where your pressure limits are. The last thing you want is to use too much pressure, which is a common mistake among newbies who get overzealous.
You want the jelq to create that feel good sensation when getting an erection. The pressure (against the tunica of the corpora cavernosa and corpus spongiosum) is what induces size increase, so you want to establish a set amount of pressure for yourself. And the farther away from the glans the less pressure it will get; the closer you get to the glans the pressure increases on the glans.
To avoid the pressure on the glans just simply reduce the pressure on the corpus spongiosum. You can do this by using a “C” grip that only clamps down on the corpora cavernosa. For corpus spongiosum and glans work you can use the “C” grip that clamps down on the corpus spongiosum, hooking around the corpora cavernosa partially.
This is all based on my knowledge of the penis anatomy, and personal experience. It shouldn’t be taken as the definitive truth.
Starting size: 6.25" BPEL (5.5" NBPEL); 6.5" BPFSL; 5.0" MEG (3/2014)
Goal: 6.5" NBPEL (7.25" BPEL); 5.5" MEG
Current size: 6.50" BPEL (5.75" NBPEL); 7.5" BPFSL; 5.25" MEG (11/25/2015)