As you get further into your masturbation session and start to get a little more excited, some fluid (technically "Cowper's gland secretion" but commonly called "pre-cum") might ooze out of the end of your penis. It's often whitish, slippery, and perhaps a little bubbly due to all of the action going on from your hand. Some guys can actually get enough of this fluid flowing to use it for lubrication. However, a large proportion of males go their whole lives without ever producing the stuff. This is normal, and there really isn't any way to get your body to produce it if it doesn't already do so.