Maintaining proper humidity is yet another reason to store the guitar in its case when it isn't being played. In many locales it's difficult to impossible to maintain the proper humidty in an open room, e.g., in a climate like matonanjin2 describes or in the dry winter cold and arid summer like mine. Note I say that with no experience with room humidifiers. Raising the humidty in the house/in a room is something I've tried to avoid my whole life.

Virtually all experts recommend a humidty of 45 - 55% for guitars. It's more important for acoustics than solid body electrics but, beyond concern for the body of a guitar, humidity (or lack of it) can cause problems with the fretboard too. FYI, there is such a thing as too much humdity for a guitar.

First step -- find out what humidty your guitar is sitting in. I use a small, cheap gauge I got from the Walmart hardware section. When in the case it fits nicely at the top of the guitar's head. If the guage shows a need for a better humidty environment do indeed get a humidifier. Second step -- do a Bing search and you'll find many different kinds; search YouTube and you'll find lots of instruction about how to build your own. For my acoustic, I use a combination; a store-boought for the body's interior, a home-made one for up under the neck.

Be aware of air conditioning. A/C can skew a room's humidty (that's it's purpose) and, even if your climate doesn't call for keeping your guitar safe, the a/c might. The same applies to some heating systems, e.g., forced air. Static electricity, those little sparks you get moving around a dry room, is a hint you need to check your guitar's environment.

Here at GT, go visit the Guitar Tech sub-forum. A search there will reveal some threads about guitars and humidifiers.

I believe, as do almost all others, that a very low humidity will eventually damage a guitar (or other wood instruments). It may take take a long time... or it may not. Guitar humidifiers and storing the instrument in its case is cheap, easy insurance.

Good luck, have fun.