Good resource/advice on mentoring undergrads
All of the below stems from my own experience mentoring and working with undergrads, both as a grad student and as a postdoc.

Firstly, realize that many undergraduate students aren't ready to do research on their own when they first arrive in a research lab. (Heck, neither are many graduate students...) Additionally, many will not want to do their own research, but they're very happy learning what you do and helping you set it up and work through it.

That being said, you'll want to start with simply talking to them during the interview process to determine what they want to gain from the experience. Most won't have a solid answer, but for the few that say something like, "I want to improve my MATLAB skills," or "I want to gain experience doing cell cultures", you now know whether they're a match for your lab.

The majority don't have specific interests, though. For those students, consider allowing them to work on a variety of projects with multiple graduate students. This allows them to observe different research techniques, different approaches to solving a research problem, and the different tools used in research. If you have the time, you (and the members of your lab) can take a more hands-on approach and actively mentor the student, showing them the various steps involved in constructing an experiment and the logic behind the data analysis stream.