There are several kinds of adhesive removers on the market. Most have a very strong odor, which can be difficult to deal with. If you have problems with ventilation in the space, or if you are sensitive to chemical odors, look for a green alternative such as a green emulsifier. Another choice would be low-odor mineral spirits, which can also be used to remove adhesive. A simple adhesive remover that works with varying results is fabric softener mixed with hot water.
Instead of just putting the adhesive remover on and getting right to work, you will need to let it set. This loosens the adhesive so you don't have to scrape as hard. Always let it set for around five to 10 minutes, or longer for stubborn areas. If you divide your workspace up into sections 3 feet by 3 feet, you can have one section setting while you are scraping the other. This helps save time.
If it's just a subfloor that will be tiled over or covered, you can use a regular drywall knife. While you don't want to scrape too hard and gouge the subfloor, you can put a little more oomph into the job. However, if the adhesive is on hardwood floors that will be refinished, you do not want to use a metal scraper. Use a plastic putty knife instead.
Once the adhesive has been entirely removed, you can restore the floor. For subfloors, you can tile over them again, add carpeting or even laminate flooring. For hardwood floors, you will need to rent a commercial floor sander to get down to the surface of the bare wood. Once you have done that, you can pick your stain color, apply and then finish the floors with a few coats of polyurethane to give it a nice shine.