Most beginning writers have a pretty good sense of correct pronoun usage, but a good editing strategy will help you make sure you have not missed any issues with pronoun agreement or pronoun reference.
One strategy is to edit your writing one time, just looking at pronouns, in addition to other editing passes. If you have had trouble with pronouns in the past, you should circle all of your pronouns and ask yourself questions about their purpose and what they refer to.
In this video, the Grammar Professor will review common issues writers have with pronouns.
NOTE: Because the use of the singular they is new, you may find some people who disagree, but most academics now agree that the singular they is correct. Please always refer to your style guide, as some style guides still recommend not using the singular they.