If you are in live realms,
oUF_Classic,
oUF_Lily,
oUF_Simple2 are some of the tutorial layouts for oUF.
You can find a list of HOW TOs with building the basic things of a layout in oUF_Simple2.
Besides, you can start with any layouts you like, too.
But it would be better for you to start with something easy and familiar to you.
If you are in beta realms,
oUF_Simple(mop) is a reference layout for beginners.
After knowing the basic things,learning from every most downloaded layouts would surely help you to improve your own.