-Use a hair dryer or a heat gun on the low setting. Take out the bulbs and blow hot/warm air from behind. You can also use the gun/hair dryer pointing at the lense but be careful...heatguns can emitt high enough temp heat to sometimes melt/distort the lense plastic(happened to me while not paying attention lol)
-Tie silica gel packs together with a string and leave them inside the headlights overnight(put in through bulb holes). Take out in morning before you go driving. You can raid your local walmart and get the two bags inside every iron if you feel to cheap to buy some lol.