If you're not sure, spend at least $200 to get something decent. A very cheap guitar is likely to sound bad, be hard to play, and in general discourage you from practicing. You might luck into a cheap used gem a pawn shop, but it's not terribly likely.
Play songs you like and can plan, and play them slow enough so that you're changing chords IN TIME with the beat. OK, so it's REEAALL SLOOWW at first. Speed comes with repetition. You're teaching your ear and your hand what the song FEELS like, in proper rhythm. One teacher I had called this "perfectly slow."
I made up a little fanfare to force myself to work on the changes I had the most trouble with. Do one yourself.
Look for the similarities in the finger patterns and economize motion. If you don't have to move a particular finger, don't! If two or more fingers have the same relative position in the two chords (for example E and Am), move them as a unit.
Lift your fingers up off the strings only enough to clear them. Lift them just enough so they're off the strings, move them, then drop back down. Don't waste energy waggling your fingers in mid-air.
Use the minimum pressure needed to get a clean sound. Don't wear yourself out. Let your fingers and thumb work together like a clamp - a very gentle clamp, just enough to do the job.
Especially when playing rhythm, the first note of the new measure - the downbeat - is usually going to be the root note of the chord. So nail the note on the bass string first, then let the rest of the fingers follow a fraction of a second later. For example, when changing from a D to a G, move that third finger out to the sixth string at the third fret FIRST so you can nail the bass G on the beat. You've then got time and a bunch of open strings (you can let the 5th string be muted if you need to) before you need to have the first string at the 3rd fret.
Play the chords slowly, one string at a time, and pay attention to whether your finger tips or nails are muting adjacent strings. You might need to adjust the position of your fingertips so that they arch over cleanly and come straight down.
That said, I recommend taking a break from chords every now and then with what I call "spider dance fretboard aerobics." These are finger exercises for the left hand that build strength and flexibility.
Do this:
First finger (index finger) on the sixth string (the low E) at the first fret. Second finger ("attitude" finger) on the same string at the 2nd fret. Do NOT lift the index finger up - keep it pressed down. Now do the third finger (ring finger) at the third fret, still on the low E. Keep the 1st and second fingers down. Feel the burn? Finally STREETTCH your pinkie way over to the 6th string, 4th fret. Make sure they're arched over so you can play a clean open A on the 5th string while holding down all four fingers.
Repeat this exercise on each string and work across the fretboard. Repeat it with the index finger starting at the 2nd fret, 3rd fret, etc. and work up the neck as high as you can reach. Play it slowly enough to play each note perfectly crisply and cleanly.
DO NOT PLAY IT BACKWARDS! DO NOT LIFT YOUR FINGERS until you are ready to move to the next string - keep all four clamped down.
You're teaching your fingers to space themselves along the frets, and making them stronger to boot. When it comes time to learn scales and arpeggios, you'll be halfway there.
The first kind is the basic 5th fret, 7th fret, 12th fret think you use to tune. You can either touch the string at the node (fret) with the LH and pick with the right, or "pop" it with the RH only - touch the node with the index finger and pick with the thumb or thumbnail.
The second kind uses that same technique with the RH, but frets the string with the LH. So you put the LH at the 2nd fret and pop with the RH at the 14th.
The third kind uses the same idea but taps on the string at the high fret node rather than popping it with the thumb and index finger.
The fourth kind is what Billy Gibbons or ZZ Top uses. Choke up on a really stiff pick (Billy uses a peso - a Mexican coin worth a fraction of a US cent) so that only a tiny tiny bit of the pick is sticking past the flesh of your thumb. When you pick the string, the thumb will immediately mute it just enough to bring out the harmonic.
Here's a slightly more technical explanation. A vibrating string is shaking at a whole bunch of frequencies (wavelengths), all at the same time. The wavelength of the whole length of the string is the primary (or fundamental)wave, and all the rest are harmonics. When you pop a harmonic using any of the methods above what you are doing is killing the fundamental-wave vibration so that the others can ring through. The harmonic at the 12th fret is an octave above the fundamental - it's exactly 1/2 the wavelength of the fundamental. The harmonics at the 5th and 7th frets are likewise mathematically related to the fundamental. The 5th fret is 1/4 the length of the string, and its harmonic is 2 octaves above the fundamental.
ANY stringed instrument displays harmonics. You can do the same thing with a sitar, a cello, a piano, a bridge. (Yes, in the 1930s harmonic vibration ripped apart the Tacoma Narrows bridge.
Fast strumming with a heavy pick will trash your strings in no time, though. So if you do a lot of rhythm strumming, use a more flexible, lighter pick. It bends a little bit before sliding off the string on the attack. You don't get as crisp an attack when playing single notes, though.
| I | IV | V | VIm | |
| G | C | D | Em | (What I call "the people's key of G") |
| A | D | E | F#m | |
| B | E | F | Gm | (save yourself - use a capo) |
| C | F | G | Am | |
| D | G | A | Bm | |
| E | A | B | C#m | |
| F | B | C# | D#m | (get a capo, or work on your barre chords) |