Arousal before a session. How important is it?

My question is how important is arousal before a session and what do you guys to achieve adequate arousal? I have not had a dry o or super o yet. I limit my masturbation to ejaculation to at a minimum of one to two days before a session. I will usually watch porn or look at some hot pictures for about 15-20 minutes and then starts session. I have a lot of dud sessions however some semi successful sessions where I have some unique feelings. Should I approach the arousal session differently? Am I not spending enough time "prepping" for a session? Or should I be doing something different?? Any advice would be welcome!!!!