If you want precision from them, you are either going to have to build or buy a spine tester and a grain scale.
If you just want plinking arrows or disposable arrows, just fletch them and put on nocks and points.
Either way, select your dowels carefully as they weren't made with becoming arrows in mind. Look carefully for dangerous grain run off. Heres how I do it...
1. Carefully select the dowels
2. straighten.
3. spine and weigh write the weight and spine on them.
4. put them into groups according spine.
5. select a half dozen or a dozen from a spine group that are within 20grns of each other. You can match them close if you want.
6. check straightness on them. Straighten again if needed.
7. spine and weigh again just to make sure. If some of the dowels weren't seasoned when you bought them, they decrease in weight and increase in spine.
8. Sand lightly with fine sandpaper. Don't get carried away as you can affect the spine.
9. Stain. I use min wax stain and a paper towel or rag.
10. outer finish. I wipe on three coats of polyurethane. I use fine steel wool lightly between coats.
11. taper nock and point end.
12. apply nocks and points.
13. fletch.
Since I have arrows of different lengths and spine groups and they all look basically the same, I put a piece of masking tape around the arrow just in front of the fletching. I get a fine point marker and write the spine, the length, the weight of the raw shaft, and the weight of the finished arrow.
You could also crown dip and crest. If you did that, you would have to do it before you applied the fletching. But that's more work and time so I don't bother with it.
Anyway, that's how I do it.