To be a good guitar hero, it's important to understand how the game works.  For instance, do you know how the game decides how many stars you get on a song?  It actually has very little to do with your accuracy--it has to do with your multiplier.  When you go to "more stats" after playing a song, you will notice that it gives you an "average multiplier."  If this number is below 2.0, you'll get three stars.  If it's over 2.8, you'll get five stars.  Anything in between gives you four stars.

To calculate your average multiplier, the game probably knows the 4x multiplier value for the entire songs--200,000 points, for instance-- then uses your score as a numerator * 4.  So if I score 100,000 points on that song, I have a 2.0 multiplier, and I get 4 stars.  If I score 140,000 on the same song, I achieve my 5 star multiplier of 2.8.  It is possible, through the use of star power, to have a multiplier greater than 4.0, but unless you've played the entire song without missing a note, it won't help you at all in the game.

Since your score is so important, it's useful to know how the came calculates that score.  Here's how it works.  For unsustained notes, the score is 50 * Number of Notes * multiplier.  So GB together on a 4x multiplier is 50 * 2 * 4 = 400.  You just gained 400 points for hitting that note.  Chords, then, give you significantly more points than single notes, and combined with high multipliers, chordal sections can be a powerhouse as far as building your score.  If you play 50 three-note chords (GYO, for example) with star power (and hence an 8x multiplier), you've just accumulated 20,000 points!

Sustained notes are different, but not that much more complicated.  Sustained note value = unsustained value + (25 * number of notes * number of measures held * multiplier).  So a two-note Chord (GO) held for two measures at full star power (8x) is worth 800 + 800, or 1600 points.  Sustained note point accumulation is linear, so if you only hold it for one of those two measures, you'll get 800 (for hitting it) + 400 (for holding the note 1 measure).

...And that's it!