My dentist told me a long time ago that I produce an excessive amount of saliva and that really helps with decent (good, I hope to say) blow jobs. I definitely do not need to use a lubricant most of the time.
I usually know exactly what I want. Meaning, for some reason there are specific times with certain guys that I say to myself, "I definitely want this guy to cum in my mouth and I want to keep his cock in my mouth after he shoots particularly as he writhes from having been blown." There is something so satisfying (at least for me) to swallow his cum and to be in control of him for those seconds after he has cum. I don't know if others are the same way.