Summarize:

If you're in a bedroom and need to vanish quickly, get down on all fours and shimmy beneath the frame of the bed. Then, lie flat on your belly or back and be as still as possible. When your pursuer peeks into the room, they won't see anything out of place.  If the bed sits on a frame that's high up off the ground, the person looking for you may be able to see you or your shadow. Hiding under the bed is a pretty common tactic, so be ready to make a run for it if you happen to get spotted. Closets are tried-and-true hiding places. They're big enough for most people to fit into easily, and sometimes even contain coats and other items of clothing that can provide extra cover. And since most people don't open closets very often, it's possible that they won't think to look for you there.  Be sure to open and close the closet door softly to cover your tracks. If you're involved in a heated game of hide-and-seek, don't go for the closet unless you have no other option. Closets are a somewhat obvious hiding spot. If your hear the person you're trying to avoid about to come into the room, dive behind the couch and kneel down to make yourself smaller. Chances are, they'll take a quick look around and leave thinking that you're not there. Make sure the couch you're hiding behind faces the entrance of the room so you won't be visible.  You might also curl up behind a loveseat, easy chair, or futon if there's not a full-sized couch around. Since their backsides are completely exposed, couches don't make great long-term hiding spots. Insert yourself into the space between the curtains and the window and pull the curtain in front of you. Stand up straight and keep your arms pinned to your sides so the person looking for you won't catch a glimpse of any suspicious lumps behind the drapery. Your feet will likely be visible under the bottom of the curtains, so consider moving to another hiding spot after a short time. If the shower has a solid curtain, pull it closed in front of you. Otherwise, lie down so that the lip of the tub blocks you from sight. When you're trying to get away from someone who's casually looking around for you, getting in the shower or tub just may do the trick.  Steer clear of shower stalls with glass doors, as these don't offer any kind of cover. Be careful not to knock over a bar of soap or a bottle of shampoo while you're in the shower, or you're as good as caught! If you're on the small side, see if there's a cabinet, alcove, or out-of-the-way shelf nearby that you can fit in. Most buildings have at least a few unseen nooks and crannies in them, so you should have quite a few options available to you if you're willing to get a little cramped.  Other examples of clever hiding places are storage trunks, cardboard boxes, and laundry hampers. Never hide in a container if there is a lock or you have to de-latch something to open it. You could lock yourself inside and suffocate, especially if you are alone and no one can hear you. Never try to force yourself into a hiding space that's too small for you. If you get stuck, you'll have bigger problems on your hands than being discovered. These spaces tend to be crammed full of boxes, old furniture, and little nooks and crannies, which can make excellent hiding places of their own. Most people won't go to the trouble of inspecting behind, under, and around each and every object, so you're likely to get away unnoticed.  Some people are too afraid to venture into attics and basements at all, meaning there's a chance they won't even be willing to go in after you. Basements and attics tend to be dusty, so breathe through your mouth to prevent a bout of noisy sneezing.
Crawl under the bed. Duck into a closet. Get behind the couch. Slip behind the curtains. Jump in the shower. Squeeze yourself into a tight space. Head for the attic or basement.