You dont say what you're using for paint..... I'm going to assume a nitro based paint as is popular for guitars.
Its fairly easy. You can wash the wood if you like, but no need to try and "degrease" the wood. I'd use Naphtha to clean residual stuff of the wood. Then you can grain fill. Sand to 320 grit. Then you can use Zinsser shellac as the bonding coat. Generally, grain fillers wont have a problem with slightly oily woods. They expand slightly and will hold very well in the pores. Shellac has the marvelous property of being able to stick VERY well to wood and filler, even slightly oily wood, and it will accept nitro with no issues at all. Paint on the shellac, sand off, reapply, sand off finer.. or use Zinsser aerosol shellac as the final layer. Zinsser shellac can be used straight, or cut with denatured alcohol. I suggest a 1:1 cut from their stock mix. Just get an empty paint can and your 1 quart of shellac becomes one quart of "mix" in the spare can, plus a half quart of full strength left over. Use a fine brush, and dont keep brushing, just put it on. Shellac will shrink into place, like lacquer, but very fast, in days not weeks. Once you have a good, smooth, very thin build up of shallac over grain filler, the paint (nitro) will go on very very smoothly, and stay put. And thats that!
FWIW, I get the amber shellac from Zinsser and use it on tweed amps and cases. Similarly cut 1:1 I usually do about 8 coats. Does tweed wonders. Since yours is going to be under paint the color doesn't matter, and... if you ever thought of doing tweed... maybe get the amber color vs clear.
And... shellac can actually be used as a bonding coat on things like metal, glass..... it really is excellent for that, and also excellent as a base coat before paint on new drywall. And it smells heavenly as well (not stinky like nitro)
