Please, NO SANDING. The cleaner/primer as well as the cement will soften the pipe/fitting allowing them to slip together very easily....all the way to the stop.
If you haven't purchased the cement yet, the cleaner/primer and cement come as a kit.
Note that this primer is purple, which is required when used in "coded" applications. If you don't wish to see this purple, you still can purchase clear primer.
So to summarize, clean/prime both fitting and pipe. That is, take the little applicator that's attached to the top of the can and brush/apply all the way around the pipe/fitting. Apply cement in a similar manner with that brush in the top of the can.... to both fitting and pipe and slip together until the pipe stops, and now give it a quarter twist and hold for 10-15 seconds until it sets. Done! You're now a plumbing expert!