for undergraduate students

If you are looking at graduate school, do some research (both with a lab and on which schools you are interested in). The process is long, the process is stressful, the process is random. Just remember there are better students than you who get rejected and worse students than you who are accepted; that's just how life works.

From the perspective of a current PhD student, undergrads who are strong candidates for graduate school are smart, motivated, and most of all curious. Read papers on fields you find interesting. Ask your professors (and TAs) who they might know who is looking for students and then go read all of those professor's papers. Read them until you not only know the mterial, you can talk about it. Then email them about a paper. It seems that emails about lab openings are sent to the trash rather quickly. Talk intelligently but not arrogently and ask about what they do and where it's going. Then ask if they have lab openings.

If you are a Purdue student looking at grad school elsewhere feel free to reach out and I can give you my take on the whole process.