Generally, I would say "with enthusiasm". Consider the reverse. When receiving oral, do you prefer a guy who enjoys and gets turned on by licking pussy, or a guy who thinks he's painting a fence and would rather be pounding nails? Let's face it, technique is useless to someone who turns in a dull, go through the motions performance. Without enthusiasm, even the best technique will be dull as well.
I've noticed that women who don't like CIM have a hard time pulling this off. It seems to me the inevitable result of being "too good" keeps them from giving it their best, because part of their mind is focused on making sure I don't cum while they are sucking me. If she is sucking me like she doesn't want me to cum?
Epic FAIL.
Number one move to appear enthusiastic? (there are many) Grab my ass with both hands and push my dick into your throat instead of just head bobbing. Repeat as necessary. The closer you get to your gag reflex, the more saliva your mouth will produce. This is a good thing, the wetter the better. Bonus for eye contact, and double bonus if I can see my dick sliding in and out of your mouth. (No bonus points if all I see is the top of your head)
Another way to demonstrate enthusiasm is to come up with variations on your own, rather than just follow the guy's lead.
Example; I used to date a girl who always surprised me with new variations that I never would have thought of. As an example, one morning she tried drinking hot tea, then switching to ice cream, hot cold hot cold hot cold. That's how I woke up, and it drove me wild.
I must say, Pop Rocks were a very odd sensation, but certainly different and fun. The point is, I never doubted for a second that she was really into it.
The best technique or trick will be different from guy to guy, but having a happy enthusiasm for BJ, and for your job in general, will be a hit with every guy you show it to.
I don't know if these are my best words, but there are a lot of em just in case!
POD