Marking off the IV and V positions on a guitar is not entirely unlike tuning the guitar. Before you begin, make sure the guitar is in tune (see Tuning your Guitar).
The IV position is the position that represents the place where you must hold down the strings on the guitar to raise each of their pitches by three notes (the initial pitch is numbered '1'; three above that is '4'). The V position is, as you might guess, the place where you must hold down the strings to raise the pitch by four notes. After your guitar is in tune, play the lowest string on the guitar with your finger pressing down hard at different places along the string, with an electronic tuner or piano or keyboard available if you think you will need it. The IV position is where you must hold down your finger to play an in-tune C with this string; the V position is where you must hold down your finger to play an in-tune D (G, A, B, C, D → ; 1, 2, 3, 4, 5 → ; I, II, III, IV, V). As you will quickly discover, moving your finger closer to the tuning knobs will lower the pitch, while bringing it down closer to the pickup will raise the pitch, assuming that you're plucking the string at the pickup, as you normally should. Once you find the positions, mark them off; you will most likely use them often while playing.
I actually used fret wire for these positions. To use fret wire, cut a very thin slot in the neck of your guitar along the line that you marked in the last step, and hammer the wire into the slot. I strongly recommend practicing on a scrap piece of wood ahead of time, to make sure you have a thin-enough saw if nothing else. This is what my guitar looks like with frets at the IV and V (and Octave (IIX)) positions:
If you are tired with trying to hold all four strings down with your finger, you can always cut out a slide to hold them down for you. The best way to do this seems to be to take a metal pipe, roughly half an inch in diameter, and cut off a segment of it that is as long as your guitar's neck is wide. This pipe section functions effectively as a slide.
To play a song, find the music for that song with I, IV, and V positions marked, and play the music, holding all four strings down at the correct position when you are supposed to play that position. For the pep band favorite "Louie Louie", which may well be playing in the background as you read this as it is embedded in the main page for this site, play the following, with each position being a quarter note and each comma being a quarter rest:
|: III , | , IV IV, | V V V , | , IV IV , :|
Repeat until the home team scores, or until someone gets fed up and starts throwing stuff at you.
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