If you play contemporary music on your guitar, you've likely tried to figure out the chords to a song before. Getting the chords right can be tough, and I'm certainly no expert. But here are a few tips that I've found helpful, and maybe you'll find them useful, too.
Tip 1: Find a basis to start with
It can be very helpful to at least have a basis to start your chord notation from. If you can at least find out what key the song is in, what some of the basic chords are, etc. that information will be a great help. One way to do this is to find a sheet music sample for the song. Websites that sell digital sheet music will often offer a free one page sample of songs. You can get the key signature and basic chords from the sample music and go fro there. If you can't find sample sheet music, try to find someone else's guitar chords for the song, even if they aren't 100% accurate.
Tip 2: Pick out the top and bottom notes
When you're trying to figure out a particular guitar chord, it may help to figure out what the melody and bass notes are. If you know the bass note, the melody note, and the key signature, you can narrow down the choices to just one or two chords. Let;s say for example that you're playing in the key of C, the melody note is a G and the bass note is an E. The chord is probably a C/E chord or an Em chord. It could also be a G6 or a CD7.
Tip 3: Look for patterns
If you can find the patterns in the music, you can figure many chords out at once, or use probabilities to figure out tough chords. Of course, always remember that variations in patterns are often used.