This helpful tutorial from the Leeds, York and Manchester University libraries introduces you to social media
The tone of the language used by you and your connections. Is the tone positive, negative, or neutral? Is this consistent with how you would like others to perceive you?
The words used most often by you and your connections. Are these words ones you would like others to associate with you?
The sources of the posts on your Facebook Wall. Are your posts coming from you, your friends, or an application you use? If a lot of them are from a game application, for example, do you want others to see that?
The timeframes of your activity. What days of the week and times during the day are you most active? If you work during the day and have a lot of activity during work hours, would this be a good reflection of how you work?
The categories of the Facebook Pages you "like". What type of Facebook Pages do you "like"? Are you comfortable with others seeing this?
Is the information in profiles across different social networks similar? Recruiters often look for discrepancies in your education and work history
Student Futures have useful information about using social media in relation to job hunting.