For example, if you keep it in a garage or in basement, I am thinking the tires might lose air and then the wheel will pressure down the tire. So do you need to check the bike once in awhile and inflate it?
I'm gonna sorta disagree with Zen on this one. If you're talking months vs years, and the bike was stored inside in a location where condensation would not have occurred (eg, not in a cold corner of a basement in a humid climate), and the bike was in good condition when stored, then all you need to do is air up the tires and wipe the dust off.
The tires and brake pads won't rot overnight, the lube won't leap off the chain. Properly lubed bearings won't corrode. Disk brake rotors (and caliper brake rims) may develop a slight coating of oxidation, but that will be worn off in the first ten miles.
If it's been stored for several years, however, you may want to squirt a little oil on the chain and give it an extra wipe, both to get the dust off and because oil does slowly evaporate. And check the tires and brake pads for rot.
Once or twice a year a bike should get its cables lubed, and the chain should be cleaned and reoiled every 200 miles or so (or at least once a year). This is unrelated to how long it's been stored, but a good time to do this is when you take the bike out of winter storage (though a better time is before you put it into winter storage).
Yes, if your bike is stored for more than a few weeks, you should check it thoroughly before riding it. The tires will lose pressure, and the chain will need lube for certain, and depending on the length of storage, rubber components like brake pads, tires, and hydraulic seals may degrade. In addition, surface rust, and sometimes deeper corrosion can develop which would require a more complete service.
Zenbike covered it, but I would also add (would comment but don't have enough rep yet!) that: - Organic Disk Brake pads can become degraded over time, especially if the bike is stored in a oily fumey environment. - In our garage / outhouse we have a problem with mice chewing through cables.. any cables they can find.. nom nom nom yummy rubber!
As with most things, regular short usage is better than no usage at all.