You know, a lot of it is genetics. Some guys are naturally long, some naturally thick, and some both (bastards). The secret to gaining girth is to do exercises that work on expanding the shaft. Jelqing at erection levels around 80% expands the shaft using pressure from your hands that works your cock from the inside out. You are constantly squeezing more blood in and slowly expanding your cock. There are variations of this movement called horses, uli’s, clamping and others that also pressurize your cock from the inside out to cause expansion.
Pumping, works from the outside in by creating a low pressure atmosphere outside your cock which allows more blood to rush in and fill the expanded spaces.
It seems, that a lot of success is obtained by combining these two different girth methods so that they complement each other. Routines that go pump, jelq, pump, jelq, pump, jelq are very effective.
But this method is also an advanced method, so if you are just starting out, you should begin at the beginning and condition your cock to the rigors of PE by doing manual stretches and jelqing for a couple of months. Starting routines are in the Newbie Forum.
Get a good start to PE, and you will end up with a great finish, girth gains and all.