The only thing that will help you is hard work. If you'd like to do work is plasma physics, you'll need a very strong mathematical grounding. Plasmas are funny things, and the field isn't too well funded. I know a couple people who have PHDs in plasma physics and they work as reactor physicists. But really, the field you get into isn't overly important if you are a curious person, for there is something interesting to be discovered in all fields.
Work hard, don't wait. Treat mathematics and physics like an art and practice it. Talk to people in the field, attend conferences on what you're interested. Those things will help you.
Undergraduate research is a strange thing. I currently work as an undergraduate researcher. The most important thing about undergraduate research is that you're able to work hard with a minimum of supervision and guidance. Good writing skills are a must. I will be lucky if I can get an hour of my prof's time a week. The sad thing is that most universities do undergrad research as a sort of marketing toy. They'll have some sort of small amount of money that they can set aside to pay students for a summer to work on various projects. Most of us get jobs operating equipment or sorting through data instead of 'real research'. The granting agencies don't count the number of undergraduate researchers you have, only graduate researchers.
I was lucky, I taught my self to write code at a very young age and I put together a portfolio in high school, so they have me writing custom software for lab equipment this summer, but I am very lucky. The guy in the lab beside me knew how to build electric circuits, so they have him working a few related projects.
But make sure this is what you really want, because it'll become your life. There isn't an hour in the day I don't do something related to 'work' (well other than eat or sleep). Everyone you'll know or have anything in common with will be from your department. You sort of take the red pill when you completely devote yourself to a field. I manage a few hours a week to go to a party or play soccer or play the guitar or something, but you really do have to be very devoted.
But if you decide to do this, put all your energy into it and never look back. The mountain that you will climb will seem insurmountable, and indeed many fall off, but if you're willing to put continuous effort into this for years, then it is well worth it.
What would really give you a leg up is having a portfolio of some sort. Write some sort of MATLAB code that solves some sort of heat transfer problem or something like that and the profs will be all over you.