How would you create uniformity in the look of the bookshelf?
First you will want to get a fine grit sandpaper and sand every piece of wood to a smooth surface.  From there, you will want to obtain a stain or oil that will create a uniform finish when you apply it evenly and equally across all pieces.  Following that, you will want to let the wood drive in a well ventilated space before evaluating if the color you obtained was what you wanted, if not, repeat the staining process until happy.