That depends. How often do you play? If you're playing every day for at least a half hour, then you'll find that the tone of your strings will deaden after three or four weeks. Maybe sooner, maybe longer. If you play a little less than that, or if you're just not sure, then it's a safe bet to have them changed every other month. You can bring your instrument in to a guitar shop to be re-strung, or you can learn how to do it yourself. It's really not that hard.
After playing, wipe it down with a clean, lint free cloth. Also, wipe your strings so they'll last longer. You can purchase guitar polish to keep the finish nice and shiny, as well as string cleaner to make them last as long as possible.
Alright, stands are okay provided you make sure of a few things. First, make sure that the relative humidity in your house is between 45% and 55%. Anything higher or lower will cause damage. Second, make sure that no children will be anywhere near your instrument. If that is impossible, then purchase a wall hanger instead of a stand and place the hanger so that the bottom of the instrument will hang higher than a child could reach.
Good attitude. Your new instrument, like your car, house, computer, or dog, needs the right conditions and treatment in order to function to the best of its ability.
There are three big factors to consider when it comes to looking after your wooden instrument:
Temperature: This one's easy. Keep your instrument at room temperature at all times. It's made of wood, so when it's exposed to drastic changes in temperature it will react accordingly. If it's exposed to very cold temperatures, the wood will contract and cause finish cracks. Those don't come out. Hot temperatures can cause glue joints to soften, and your fretboard can crack and pop up. Don't keep it in the car, and don't let it get exposed to direct sunlight or heat sources or large explosions. Or lasers.
Relative Humidity: This one's pretty straight forward too. When your guitar was created, it was dried, seasoned, and acclimated to a specific relative humidity (RH). A guitar is at its happiest when the RH is between 45% and 55%. If the RH goes below 45% you may find some major problems beginning to occur as a result of your guitar drying out. Here are the symptoms:
How these problems are corrected: a truss rod adjustment (the truss rod is the piece of metal that runs up your guitars neck), and the insertion of a sound hole humidifier or a case humidifier for some intense re-humidifying. We wouldn't recommend readjusting the neck yourself. That sort of thing is best left to professionals. It's a very delicate process, and taking the truss rod too far in either direction can do more damage than good.
The re-humidifying, however, can be done with relative ease. You can use either a sound hole humidifier for acoustics, or a case humidifier for electrics. It can take as long as three or four days to restore your instrument to an acceptable humidity, so don't get impatient and soak your instrument in the tub. Bad.
It's a very good idea to bring your instrument in to a guitar shop for a check up at least once a year or even better at the changing of the seasons (when temperatures and humidity naturally change).
Domestic Violence: This is where we tell you to be nice to your instrument. Don't kick or punch it. Don't drop it. Don't strip the finish and re-paint it. Don't cover it with stickers. Don't let your uncle who's been in to the "juice" get up and perform an air band version of Thunderstruck with it. These are all bad things. Pete Townshend smashes guitars, but keep in mind that Mr. Townshend can buy new guitars like we can buy chewing gum. The best place for your instrument to be (if it's not in your hands being played) is in a case.