The first thing you want to do is clean house. Double ugh, I know. But, especially if you have kids, you won't know for sure that one of the things that the pesky buggers are getting so excited about was the rotting pear in the couch cushions or the plum hidden in a end table cabinet (not that I'm speaking from experience, of course. *snort*) unless you do a thorough job cleaning out all possible places they could be hiding.
Now they'll be stuck hanging around more obvious places like around a sink full of dishes or a trash can that needs emptying. You'll want to take care of those too. Make sure the dishes get done daily (no excuses!) and, ideally, as soon as they are dirtied. Designate one trash can in the house as available for anything with any sort of food traces on it and take that out the most frequently--ideally every day. If you are like our family, you may find it hard to justify that tiny bit of trash going out every day (our family of 5-6 usually only has 1 to 2 large trash bags a week to put out for the garbage collector), so you might want to make this designated trash area a super small trash can and use plastic shopping bags for liners. These tiny bags can then be taken out daily with no guilt and put in a larger bag for the garbage collector at the end of the week if there is a limit on how many bags you can put to the curb.
The next phase of your attack is a two-prong assault. You'll want to use a vacuum cleaner to suck up any flies you still see flitting about. Make sure you change your vacuum bag after each use so they can't breed in the bag. Seriously, ew! Plus, you'll want to change the bag outside so they can't escape and be free to fly around your house again. If you have a water trap vacuum like a Rainbow, that's not a concern though, since they are dead in the water as soon as you suck them up.
|My ugly yet effective fruit fly trap|
After your aerial attack with the vacuum, you'll want to set a trap for anything that remains, because you know you didn't get them all! You can make a trap by putting 3 parts of water with 1 part of molasses and a pinch of active dry yeast in the bottom of a jar and putting a funnel over the top so they can get in to their yummy food of death, but they can't find their way back out. I use a jar with that I'm not going to want any more with a paper funnel taped to it so I can throw it away (taken directly outside so we don't have any escaped prisoners) and not have to worry about them escaping back into the house.
Repeat the vacuuming step as needed whenever you see them flying around and keep up one the trash and dishes and you'll notice the population going down pretty quickly. One day soon, you'll even realize it's been a while since you've seen any fruit flies and relax knowing that you once again have a fruit fly free home.