One of the easiest ways to combat pesky mosquitoes is to be vigilant about standing water. Mosquitoes need only a spoonful of still water to leave their eggs behind. While it's obvious that places like buckets, kiddie pools and inactive birdbaths are key real estate, consider less-obvious places like uneven gutters or the small trays under planters. If you do find an area that is difficult to dump or dry out, add a little vegetable oil to the standing water. It'll effectively kill the larva that may be inside.