Alexus' general rule of thumb, when applying by hand:
Liquid = circular motion.
Paste = up and down motion.

Although Meguiars' will always reccommend a circular motion to apply the wax.

I generally apply a paste wax using my bare hands. The heat generated by your hands activates the wax and makes it more spreadable. Using your hands and fingers also allows you to be more precise.

Try adding a couple drops of water to the applicator to make it easier to spread.

Meguiars' reccommends keeping any and all moisture away from the vehicle. The wax will not cure properly if it is particularly humid outside, much less if you're adding water to the applicator pad. :P

Where did you see that information? I can't find that!

Car Wax FAQ. How to protect your paint with a good coat of car wax.

^There's a bit in that article that says that wax will not dry properly in humid or cold weather, so adding moisture directly to the surface of the car won't allow the wax to dry and cure properly. I know this mostly from experience though. This is why the "wax-as-you-dry" products such as QuickWax do not offer a whole lot of protection. They never properly dry.

^cool,thanks!