Each term, identify a faculty person whom you would like to get to know better. By doing so, you'll learn what it takes to get a Ph.D. and show the professor that you are seriously interested in advanced study. Later on, this will help that professor write a strong letter recommendation on your behalf. The worst thing you can do is to wait until your last year and be forced to ask for letters form professors who can hardly remember who you are. Practice graduate school habits now.
Graduate school can be intense.
Start preparing by making yourself go the extra mile. Choose to read the extra credit reading in one of your classes. Remember that graduate schools look at the composite. Just because you don't have a 3.0 GPA doesn't mean that graduate school is completely out of the question. Grad schools look at your cumulative GPA, your GPA in your major courses, and your GPA in the last two years.