This famous song is in open G tuning:

Low D:G:D:G:B:D

Use fingerpicking to play the strings, but country style - not classical. That means resting your thumb on the bass strings and keeping your fingers resting on the higher strings. This serves the purpose of allowing you to quickly mute the strings after picking them simply by bringing them back to rest on the strings. This is particularly important in this song. Much of the muting is done this way.

In particular, keep your thumb resting on the 2nd lowest string (G in this tuning) even while picking with your other fingers. Of course, pick with the thumb when needed. This technique allows you to control string noise, and mute effectively to get nice choppy riffs.

The best way to learn this song is to break it down into the main riffs. There are sometimes variations within riffs, and you can learn those here. However, if you want to just get the main parts, then work on the following segments:

Riff 1 - Simple stuff for starters. Keep your thumb on the G string whilst picking this, and after you pick the strings with your 1st and 2nd fingers, bring them back to rest on the strings. This will mute them. You can also mute with your fretboard hand as we show here.

Riff 2 - This part is more fluid, and you need to pick with your thumb and 2nd finger.

Riff 3 - At the end of this riff, move up to play this C chord. Later in the song Keith plays it by fretting a fuller chord - like here. If you aren't too concerned about perfectly replicating the song, then use which one you like best.

Riff 4 - This is similar to Riff 2, except it ends by shifting up through a couple of barre chord shapes.

Riff 5 - Again this is just variations on the earlier riffs leading up to the chorus.

Chorus - Just alternate the chord shapes shown. Mute between strikes with both hands as discussed earlier. Also, you can strum with your fingernails in places (like here).

The rest of the song is just more of the same riffs, sometimes played with flourishes and variations. If you know these main riffs the rest will be easier to learn!