The more expensive the guitar, the more care it needs, but even low priced instruments need some care. As guitars get older they get more stable but always need at least minimal care.
When new, your instrument should be set up or adjusted by a Luthier or Professional Repair Person. It doesn't hurt to have the guitar checked after every major seasonal humidity change.
Keep your guitar clean. Fingerprints and foreign matter on the finish can do damage if left there too long. There are lots of guitar polishes on the market, but very few are true polish. Real polish contains a fine abrasive material, usually talc powder. Using real polish will remove small amounts of finish. Polish and wax are only used at certain times and those times are ALWAYS by a Luthier or Repair Person (L/PRP}.
What you want is a mild cleaner. I use S.I.T. brand in the shop but there are other good brands to be had, ask your local L/PRP. When you use a cleaner always spray the polishing cloth, not the guitar. Spray the cloth, wipe the guitar and then follow with a dry cloth. This is especially true with vintage instruments.
Treat your guitar like a small child, if you wouldn't treat a child that way then don't treat your guitar that way.
Acoustic Flat Top and Arch Top guitars require humidity in some regions/seasons. Having a digital hygrometer in the room you keep your guitar in will tell you when humidity is needed. Acceptable humidity levels vary with region so talking to your local L/PRP will help you understand what the hygrometer is telling you. (Click here for instructions on making a humidifier for your guitar case)
Storing your guitar for short periods fully tuned in not a problem . If a guitar must be put in storage for long periods it would be best to de-tune it. If it is a steel string with a truss rod it would be best to have the truss rod loosened and strings de-tuned.
Find a good L/PRP in your area and get to know them, they will be more likely to give you good/free advice if you are a regular customer. They will also get to know your guitar and may be able to spot problems before they become problems.