I think every illustrator book has a chapter on the pen tool. But, what helped me most reading the quick instructions in illustrator help as to what options the pen tool has and then reading about bezier curves in general.
As with everything else, practice makes perfect. Practice traceing and drawing basic shapes first.
Yep, tracing letters is a good way to improve Pen Skills. My favourites are a lower case italic 'f' or 'g'. Then compare points with original outlined letter.