Firstly, the glue residue, wipe with cloth soaked with white spirit, to soften the residue. Scrape away gentley with a sharp blade, and finally go over with another cloth soaked in white spirit to remove any remains of glue residue.
When bats are snaded in the factory they are belt sanded, but most people are going to have access to an orbital sander, either one that take a rectangular sheet of sand paper, or a palm sander that takes sanding sheeets that are roughly triangualr in shape. Either will do a decent job.
You will need a selection of sandpaper grades, from coarse to fine. Start with something like 100 grade and work to finer grades. If you want a really smooth surface, finish with very fine wet and dry (obviously used dry on wood) You can get as fine a 600 grade with this.