Welcome to the forum pierce_rich! It is so nice to have someone register and post in the hour!
Masturbation before jelqing would defeat the purpose...during jelqing you want to be able to maintain at least a 70% erection and this may be impossible after climax. As far as the stretching portion of your workout masturbation may actually help you. When stretching you want to remain completely flaccid and a perfect time to stretch is after climax.
I remember when I first started to Penis Enlargement I was so confused about the errection thing. I had no idea how I was going to keep a 70% erection. Everything just seemed so difficult. After a month into my Penis Enlargement I was able to master most of it. Just stay involved here and ask any questions you may have. You too will master this.