These free grids and lines are super helpful in lettering because you can make sure your letters are a uniform size and all on the same line.

The Rule Brushes
One is based on college rule, though you can scale it to any size. The other is a wider rule that reminded me of that paper we used to use in elementary school.
Download the quick rule brushes in the zip file here.

The Dot Grid Brushes
One has small dots, the other has larger dots.
Download the dot grid brushes in the zip file here.

View examples here: