Research experience never hurts. Start looking at externships in your area of interest, but it is fine to have different experience as well. If there is an area you know you have more interest in, doing 2 externships in the same area could be good. HOURS, all internships have a min. hours cut off, the more clinical hours you accrue, the more internships you can apply to.
Depending on the program and whether they allow it, students will take on an extra practicum or find other experiences. My peers conducted forensic and neuropsych evaluations at our local court system. Apply widely (geographically), it's one year, even in the most "undesirable" location, most people can make it work. Late in your 3rd year you can start looking at the APPIC site and seeing which sites get low number of applicants.
Good letters of references. Ideally, try to finish your dissertation before the start of internships. Work on your personal statements early. Get to know or become friends with upperclassmen in your program. I've noticed some internship programs will take students from the same program because they trust the training from that specific academic program. Also, sometimes former interns can put in a good word for a student who's applying that cycle. Last advice is prepare for the interview. Practice with people, talk to former interns at that site, have good case vignettes, have good questions, learn about the site, and not sure how to phrase this but have decent interpersonal skills.