Combine boric acid, sugar, and flour in a dish, and place it near suspected roach entryways. They'll transport it back to their nests, and poison the others with it there. The old-time roach trap is also quite effective. Simply apply a layer of grease to the inner surface of a beer bottle with a little stale beer in the bottom. Place it near the suspected entryways, and check it daily, emptying when necessary.
Ants Use talcum powder or chalk as a barrier.
Fruit flies Obviously, use your fruit before it begins to decay. But fruit flies also like house plants. Repeat every other day until all the flies are gone To keep them hydrated, mist your plants with a sprayer of plain water daily, trying not to get the soil wet. The nicotine spray is toxic to pets, so don't use it on plants that your pets may come in contact with. If the above method fails, your infestation may need an added step.