Here are a couple helpful hints:
among/between: Among is used for three or more entities: Many local runners are among those training for this weekend's race. Between is used when two entities are involved: There is an intense rivalry between the two schools.
fewer/less: Fewer refers to people or objects that can be counted; less refers to general amounts: Fewer technicians means less work will be done today.
its/it's: Its is the possessive form: The board forwarded its recommendations. It's is a contraction of it is: It's time for a party.