Valerie is originally in the key of Eb major, however, the best way to play it on guitar is to use a capo. After sampling it on the different possible frets (1st, 3rd and 6th) I found the best solution was to put the capo on the 3rd fret and, thus, all the phrases can be played in the open C major position.
The song has three parts. In the PDF they are named as A, B and C. Parts B and C always repeat the same, except that the C part has a slight variation at the very end of the song. The A part has six variations and might be a bit more challenging to memorize. The first two variations appear at the beginning of the song and other four in the mid section.
I suggest you practice the parts and the variations separately, as single exercises, and connect them once you have mastered them. I find that when I break it down first then it's much easier to memorize.