This guide is really suited more towards those who have cheaper pianos, possibly the kind that are infrequently used (aside from possibly your kids banging on them). This is the category I was under. I know if I were to damage something or make a mistake, it wouldn't be the end of the world. The piano itself was purchased from a garage sale, cost only a couple hundred dollars, and wasn't worth the cost in having professionally tuned. That being said, it was badly out of tune, and I thought it would be worth it to give it a go.
Time for the standard "disclaimer". I am not going to be held responsible if your piano ends up damaged, in worse shape, or rendered unusable as a result of anything written here. Everything you do is entirely at your own risk and your own expense.
A little more about the tools... You can buy the professional tools, or 'make' your own. Below is a little more detail about each tool, and the professional and home-made options. The "best" option (in my opinion) is in green.
Device to adjust the pegs (tune the piano) with - If you've ever seen a guitar, you've probably noticed the 6 little tuning knobs at the end of the guitar. Turning these knobs one way tightens the string giving a higher pitch, and turning the other way loosens the string, giving a lower pitch. A piano has similar pegs (which you must find), connected to the piano's strings. These are the pegs you will be adjusting. They are almost always square.
Method to provide notes, or an electronic tuner:
Tool to pick the strings, or tuning wedges - On almost every piano, each key connects to a hammer that hits between 1-3 strings. In the cases of 2 or 3 strings, each string has to be tuned. Unfortunately, when tuning, you can't simply use the piano keys, because you have to tune each string one at a time. You therefore have 2 options:
Click on any of the above pictures to open a full-sized picture in a new window. These are the tools I used - A vice-grips with a socket for adjusting the pegs, an electronic chromatic tuner, and a guitar pick to pluck the strings as I went through.
Tuning the piano
Now that you have your tools ready, it's time to start tuning! It's usually recommended that you start in the middle of the piano (middle-C for example), but I suggest starting at the low end, because if you manage to break something, it's not the end of the world. After you've done a few keys and are comfortable, feel free to jump to the middle and work your way to the ends from there. Note that electronic tuners often have trouble reading notes at the high and low ends, so if you bought an electronic tuner, you may have to tune by ear for those notes.
To tune, you simply hit a key/string on the piano. Using your electronic tuner or source of the "desired" note, you determine whether you have to make the string higher or lower in pitch. Using your tool of choice, you then either tighten or loosen the peg very slightly and check again until you have the desired note. Ensure you make small adjustments. If you're turning the peg and the note's not changing, you're on the wrong string. Once you have the first string adjusted, move on to the next.
Note that this process can easily take a couple hours or more. If your piano needed a lot of adjustment, it may go slightly out of tune again quite quickly and might need another tune-up again within a couple of weeks. However, the 2nd tune-up will usually be sufficient, and from then on you will probably only need to tune 1-2 times a year.
Click either of the above pics for a full-sized pic. These are pictures of the tuning pegs themselves. You can also see where the strings come down. Remember, some piano keys use 2 or 3 strings. Not only do you want them all tuned, but you want them all the same, or it will sound like 2 separate notes being hit when you strike a key.
Piano tuning can be done cheaply, but it requires patience, and care to make sure accurate adjustments are made. As with doing anything yourself, there is always risk, but the reward is extra money saved, and if you end up becoming really good, the best sounding piano you could possibly have.
Disclaimer: All information on this page is to be taken as opinion and not as fact. I disclaim all liability for anything that happens to anybody as a result of this existence of this page, any other pages on this site, or any other companies, people, places, or pages, that have been mentioned, referred to or linked to. Use this information at your own risk.