"Wood grain filling" used to mean mixing sanding dust with glue to plug a hole, which certainly had its drawbacks. Today, you can rely on advanced ready made wood fillers and putties made with wood flour and binders to fill cracks or holes and use as surface fillers to level pores. These modern wood grain fill products patch evenly and allow the dried product to be sanded more readily than a wood dust & glue mixture ever could.
Abatron LiquidWood, Abatron WoodEpox, and Gorks Goodfilla Water Based Wood Filler are great wood fillers that will help you create the perfect surface you are striving for. We get wood finishing questions daily, checkout this Q & A on Using Wood Filler and browse through other wood finishing tips in Workshop Wisdom, our woodworking search engine.
If you are uncertain about finishing your woodworking treasures, consult an expert like Bob Flexner, author of Understanding Wood Finishing, a "must read" for woodworkers!