On the list of exciting things about playing the guitar, cleaning is probably near the bottom. However, it's incredibly important if you want your guitar to last a long time! It's your baby after all.
And it's really not that hard or time consuming. It's a few small basic habits that only take a little energy while you're already doing something on your guitar (you'll see what I mean).
Wipe Down Your Strings
The first thing I think about is the last thing I do before putting my guitar away. After every practice session I wipe down my strings. Our fingers have naturally occurring oils, acids, and general dirt on them. When you play guitar all of that gets on your strings and cause them to lose their brilliance and tone.
One way to make your strings last a bit longer (saving you some money) is to wipe them down after you play. You can also help before playing by washing your hands. That will transfer less of the oils, acids, and dirt to your strings.
Strings will degrade over time no matter what you do, but this will give them a longer life!
Polish Your Guitar
Those oils, acids, and dirt aren't reserved just for your strings. They get all over your guitar too. Not to mention dust and dander that floats around in the air. This is especially true if you keep your guitar out on a stand for easier access.
I wipe my guitar down every time I change my strings, or whenever I feel it needs to be cleaned. Some people use a little warm water and a polishing cloth to remove smudges. I know some people use furniture polish, though I haven't tried that personally. Guitars have a different finish than furniture, so I'd be cautious doing this.
I would just make sure you stay away from any harsh chemicals. Using a polish made specifically for guitars from a reputable brand is your best bet. There are a ton of options and they only cost about $8 or so. That and a polishing cloth or microfiber cloth are all you need!
Make sure you clean your headstock too! It's much easier to do when your strings are off.
Clean And Condition Your Fretboard
You might have seen this one coming. Just like your strings and guitar body, all of the same gunk gets built up on your fretboard. But unlike your guitar body, most fretboards don't have a finish. That means the wood is more likely to dry out over time.
I use a 2 in 1 cleaner and conditioner made specifically for guitars. Search for "guitar fretboard conditioner" on your favorite online search engine and you'll see a lot of options. Some people I know use lemon oil, but since I haven't used it I can't personally recommend it.
Condition your fretboard while your strings are off, at the same time as polishing your guitar's body. It's really easy. Just apply a small amount of fretboard conditioner all over your fretboard, and wipe it off with a lint free rag. This will both clean the gunk off and hydrate your fretboard.
An extra credit step I do every 4 or 5 changes is do this same process, but use a very fine steel wool (either #0000 or #00000). Make sure to get your frets. This will clean and hydrate your fretboard AND polish your frets for smoother playing.
Just make sure you don't do this if your fretboard has any finish, or it can rub it off over time.
Change Your Strings Regularly
I'll be the first to admit that I leave my strings on too long. But there's nothing like a brand new set of guitar strings!
So how frequently should you change your strings? It depends. It depends on how much you play, if you keep your guitar in a case or out on a stand most of the time, how often you wipe the strings down, and a few other variables unique to you.
My guideline is about every 3 months. Over time, all of the oils, acids, and dirt collect on your strings weighing them down. Even if you wipe them down after every session (remember, that extends the life of the strings, but you'll still have to change them). Not only that, but they'll eventually stretch out too much and wont stay in tune.
So the short answer I suppose is that they'll sound bad and wont stay in tune!
I know people who are diligent about changing their strings every 2-3 weeks for the freshest tone. You'll eventually develop your own schedule based on what you hear and feel. But for now try not to go longer than 3 months.
I'd also caution you against just changing one string at a time. If you break a string after only a week or two of playing a set of strings you can probably get away with it. But the older your strings are, the more contrasting the new string will be to the rest.
Be Aware Of Your Surroundings
The last idea is about keeping your guitar safe and sound. And it's simply this: pay attention to where your guitar is when you're not using it. Not if you're storing it for months in a case in a closet, though we'll cover that too. I'm talking about a day to day basis.
The optimal condition is to keep it in a case away from prying fingers, especially if you have younger kids in the house who might be old enough to get into things. I know for me I need as few barriers to entry or I can get discouraged from playing guitar. So I like to keep one or two out on a stand. I also don't have small children in the house so I don't have to worry about that. You might need to worry about pets, and you'll need to clean it more regularly if you do this. But I find it helpful to practice more, if you have the option.
Humidity and temperature are also something you should be aware of. Keep your guitar in a room that doesn't have wild swings in temperature or humidity. That means keeping it away from windows and direct sunlight too. If you live in a really dry climate, like Arizona or the Central Valley in California for example, you might need to invest in a humidifier to keep in your case.
Believe it or not, guitars need some moisture. If they get too dry they can develop cracks. Conversely, if you live by the ocean and there's naturally a lot of humidity you might need to get some silica packets to throw in your case. If your room is constantly humid, you can also look into a dehumidifier for your room.
A Few "Don'ts" About Storing Your Guitar
Now that you know what to do, here's what not to do with your guitar.
Don't leave it in direct sunlight. The direct sunlight can do a lot of bad things to your guitar. Even if your room is cooled, the sunlight can warp the wood, mess with the finish, or cause it to rapidly shift.
Dont leave it anywhere with big environmental fluctuations. Like rooms humidity and temperature swings.
Don't leave it in your car. There's almost no good season where you can get away with this.
Don't lean it against a wall or desk. Besides being bad for the neck, Murphy's Law says that someone is going to knock it over. I've seen a lot of guitars destroyed because of this very thing.
Don't keep your guitar right by a window, fireplace, radiator, or any other appliance that heats or cools. Even good windows can have large fluctuations in temperature and humidity around them. And there's typically a heater by the window anyway, which is also bad for your guitar to be stored around.
The last thing isn't a don't, but is important. As a general rule, just try to keep your guitar protected from everything around it. If you're carrying it from your house to your car in the rain, make sure it's in a case. If you get water on it, dry it off right away.
All of these tips will make sure your guitar stays healthy and in good working condition for years and decades to come.
If you want to find out more about caring for your guitar, check out this live Q&A I did a little ways back. There are time stamps listed so you can jump to specific questions you might have.