Having a curve in your erection is caused from having a weak Corpora Cavernosa which allows the shaft to bend a certain direction because of the weaker cell walls. This problem can be easily dealt with using the Jelq.
This exercise strengthens your Corpora Cavernosa on both sides of your penis, and will start to form a straighter penis after several months of daily exercise.
Jelqing for a straighter penis -
Though this exercise is basically the same as you have read before, there is a little "twist" you must utilize. Begin jelqing just like you have before, grasping around the base of a partial erection, squeezing fairly tight and sliding it to your head, repeating with the other hand. Every 5 or 10 jelqs, milk your penis against the curve, bending it the opposite way as you milk down to your head, This will begin to not only strengthen your shaft, and also help strengthen the wall that's curving, slowly training it to bend the opposite way.
As you milk down, really concentrate on your penis rebuilding with each stroke. Concentrate on visualizing your penis expanding and straightening every time you milk, taking deep breaths through your nose and exhaling through your mouth. With each breath you breathe in, visualize a ball of energy growing and and expanding in your stomach and chest. Once you cannot breath in any more, exhale and visualize the ball of energy flowing down and out through your penis as you continue to milk strongly. You will find that results will come much faster when you do this.