For mosquitoes, eat less salt, use unscented products, keep dry, lessen sweet foods intake (sugar/fruits), and wear dark colors. These little things will HELP prevent mosquitoes, but not 100% of the time, and many may be out of your control at any one moment.
Supposedly vinegar works when lightly applied to the skin, I have also heard peppermint oil works, garlic (when eaten) prevents the little bitches as well.
Finally smoke prevents mosquitoes to a degree, so if you smoke then you have that, if not then just burn some incense.