It's a phrase in scholarly writing, but in conversation it can be used as a complete thought as the verb and subject are implied. "Protip" and "lil" are words used in diction, as if I were to be saying these out loud, I would shorten "little" for emphasis and use "protip" as internet slang. Both are perfectly acceptable in the form of writing done on an internet forum for personal pleasure. However, if you would rather, I will exchange the more friendly nature of my posts for scholarly, proper writing.