Ideally, especially because it's dry and cracking, you'll want to seal it first, both sides, especially if the wood depth on the thinner side.
I use this:
Zinsser Universal Sanding Sealer.
Give it a few coats, lightly sand it in between.
The first coat, make a lot thicker than the others. It will take longer to dry, but not forever. When it is
fully dry, use about a 400-grit sandpaper to take the tooth and shine off, do another light coat, let dry, sand again, and maybe a third. Light sanding, dry, then paint!
Hope that helps. That might sound like a lot of work, but it will preserve it perfectly. I can show you some some of my wood-painted pieces if you want. They are all sealed.