Several different ways, depending on the plant:

Thin-leaved plants, such as scheffleras or peace lilies, will wilt between waterings if they aren't getting watered often enough. Best advice there: don't let them wilt--feel the soil every day until you get an idea of their rhythms in your house, and water the day before they would wilt. Especially important for plants like some ferns or Pink Polka Dot--their leaves are so thin there is only a matter of minutes between wilting and foliage damage! Even the less sensitive ones will look sad if allowed to wilt too often.

Leathery-leaved plants, like Aglaonema or Dracaena, may wilt between waterings, but more often just look a little dull and droopy. The same rule applies: water before they wilt, but not so often that the soil stays boggy. Sometimes the weight of the soil is your best guide to watering them: pot feels heavy, don't water; pot feels light, do water.

With succulent plants the best bet is to let the soil dry out completely between waterings, but not to the point that the succulent parts start to shrivel--watch for wrinkles! I usually feel the weight, and also feel the drainage hole to see if it is dry enough. Succulents usually deal with too little water better than they do with too much.

No matter how often you water your plants, the amount is the same--enough to saturate the soil and run out the drainage hole, then allow all of the excess to drain out, before returning the pot to it's saucer, or decorative outer pot. If you can't move the pot to water it, be sure to suck up any excess water from the saucer or decorative sleeve with a bulb baster shortly after watering.

Hope this helps!