I ditto @hug_of_war and @Steven0512 . I’d also offer your first lesson for free to get them coming. If you have the ability then I’d also offer free food because nothing brings a college student in like free food. Seriously.
Another point of information, however small, I’d keep in mind is that college-student time is often later than standard time. So expect them to be late so you don’t become too frustrated with it.
Advertising shouldn’t be too difficult. There are tons of billboards on most campuses. If there is a multicultural center or student group wing then I’d target those as they are often missed. The computer lab and library and eating centers as well.
Also most college students do not have reliable transportation so I’d arrange to meet on campus or somewhere central. You can also contact the specific department of your subject matter so they have you as a reference. I know we referenced people when I worked in the Math Department and the Multicultural Advising Office.
I know that most college students will bring their coursebook and you will help them with that. Sometimes with specific homework as well. You can usually check out the coursebook at the University library (or as a non-member you may have to read it there). You might also contact the department to ask if they have a spare you could use. I might devote half the time to a “lesson” of your choosing based on where you think they are. And the other half the time to their specific homework or lesson they are studying for.
Here are some tutoring fees from the college I graduated from a couple years ago.
http://als.uoregon.edu/services/tutoring/tutoring.html
I hope it works out for you!