I have always used oak for my necks, and at first I was always frustrated that no matter how well I sanded the wood, the oak's open pores meant that the finish was never completely smooth. After a bit of research I came across grain filler, and ordered a tin of Rustins.
Grain filler is different from wood filler, which is used to fill larger voids in wood. It comes as a thick putty which you thin down with white spirit (mineral spirits) or turpentine to the consistency of cream. You then apply it to the grain of the wood and it does a pretty good job of filling in the pores. I use the 'natural' version for oak, but they do other shades for darker woods etc.
The same neck after an additional 6 coats of Tru-Oil, then a final 1200 grit wet sanded coat a week later. Lovely and smooth! I hope this helps.