Here is one that is specifically about bathing:
Parrot Grooming
Bathing
Regular bathes are essential for your bird to have healthy, vibrant plumage and will also help to keep dust down produced by some species. Some birds are more enthusiastic about bathing than others so several techniques may need to be tried to find which your bird prefers, they should have the opportunity to bath at least once a week preferably more, especially in hot weather. Only plain water should ever be used, lotions and potions are unnecessary and possibly harmful.
Some will readily bathe themselves either in or out of the cage if they are given a shallow bowl of warm water. Several of the parrots I work with take a bath in their water bowls as soon as I place fresh water in them the water should be changed right after so they have clean water to drink. Placing a treat in the water can help to entice your bird in if it seems reluctant, never force your bird to bath in a bowl of water if it doesn't want to. Bathing can be an exciting time for them therefore it may be a good idea to allow your bird a few minutes to calm down afterward to avoid any over-excited nippiness.
Other birds don't feel so comfortable bathing in an open bowl of water introducing them to bathing by misting is a great way to get them used to it, use a clean sprayer that has had no chemicals in it, a new one that has been washed out would be ideal. Start with a fine mist and change the force of it until you find one your bird prefers, I've found a relatively coarse spray that is aimed above the bird so it falls like rain is preferred even by the most reluctant bathers. An alternative to the sprayer is to take your bird into the shower, there are perches that can be fitted to the walls of the shower while these work for more confident birds, nervous birds would prefer to be on your arm where they'd feel more comfortable and under less of a threat. As your bird gets used to being sprayed it will spread its wings and tail to catch as mush water as possible, how much to spray your bird will depend on them, some love to be soaked while others prefer to get slightly damp.
Baths in the morning or early afternoon are best, allowing the birds feathers to dry completely before it settles down for the night and it gets cooler.