Use pure water to water your plants. You should only ever use pure water - distilled water, deionized water, and rainwater are all viable options.
Give your plant the water it needs. During the growing season, your plant’s soil should never be completely dry. Try to keep your plant’s growing medium so that it is moist to the touch (not soggy).
The tray method of watering is the best watering method for an actively growing plant that is in direct sunlight. Your plant should be in a pot that has drainage holes in the bottom. Place the pot in a tray that is filled with water. Your plant’s growing medium will absorb the water, giving your plant all of the water it needs.

Fertilizing Venus Fly Traps is also not recommended. The fertiliser will burn the roots and likely kill the plant.
If you do decide to feed your plant a dead insect, you should place the insect in the trap and then gently rub the trap every 20 or 30 minutes until the trap seals fully. Rubbing the trap makes it think that the thing it has caught is moving.