Honey, use your hands AND your mouth!! All guys like it differently, but I haven't found one yet that only wants a mouth on his cock and no hands whatsoever.
There's no real need to unhinge your jaw like a cobra to get the guy off. I mean, it would be handy if we could, but also probably a tad bit creepy. So, take him into your mouth as far as is comfortable, and use your dominant hand to jack the rest of the shaft at the same time. Some guys like opposite rhythms (mouth and hand meeting mid-shaft and separating to either end), others like the hand to be an extension of the mouth so keep your thumb and first finger close to your mouth as you bob and weave.
Also--while I love spit as a lube, I find it dries up too quickly. Find a lube you don't mind the taste of. (I think Astroglide tastes gross but I love Durex's Tingle stuff--and it makes me minty fresh!) Use that on your hands to help with the sliding.
And don't just bob up and down. Get into it girl! Twist your hands, twist your head, work every inch of that cock and work it in several different directions. He'll pop in your mouth and call you Princess, I promise.