@honza992 was concerned about glue witnesses in his butt joints (Pipe down you lot at the back!).
I described a process for mating matching parts that is more often used in metalwork. In short; when you've cut your timber, rub the mating surfaces together. Use short strokes with a firm pressure to keep the mating surfaces square to each other. Then take down the high spots (where you see a shine from rubbing) with a scraper until you've got even contact across the joint.
If you have a plane and a shooting board however, I'd recommend that above all else.