Watch the I IV I V Progression in E online guitar lesson by Brad Carlton from Guitar Lab: Vertical Soloing
Melodic moves are covered in this lesson. The E note is the root of the I chord (E) and the 5th of the IV chord (A). The G# is the 3rd of the I chord (E) and it would move up a half step to become the root of the IV chord (A). The B is the 5th of the I chord (E) and it would either move up a whole step to the C# (3rd of the IV chord) or down a half step (root of the IV chord). Notice how we restricted our study to only chord tones. This same approach is applied to the I V chord change in this lesson. You will then have some really solid melodic moves to apply to this I IV I V vamp in E.