Lookup and look up
“Lookup” is a noun that means “the process or instance of looking something up; especially the process of matching by computer the words of a text with material stored in memory” (Merriam-Webster Dictionary).
“Look up” is a verb. “I’m going to look up the address.”
The same distinction holds true for “hookup” and “hook up.” The single word is the noun.
Anyway and any way
“Anyway” means “in any case.” “I am going to go to the party anyway.”
“Any way” means “a way.” “Is there any way you could drive me to the party?”
Awhile and a while
Both “awhile” and “a while” mean “for a short time.”
Use the two words if they follow a preposition. “He wanted to nap for a while.”
Otherwise, use the single word. “She plans to be gone awhile.”
Setup and set up
“Setup” is a noun, often meaning the way something is arranged. “The setup worked well.”
“Set up” is a verb, meaning to put together or “establish something.” “He is going to set up shop.”
How can you remember this? Mentally replace “setup” or “set up” with “setting up.” If the sentence makes sense, use two words. If it doesn’t, use the single word. For example, the sentence “he is setting up shop” makes sense. “The settingup was all wrong” does not.