Talk with the admissions departments of the universities you're thinking of applying to and find out what percentage of accepted students have around a 3.0 GPA. This can give you an idea of your chances for acceptance with each of the schools you choose to apply to.
Study hard for the standardized tests you need to take to apply to various universities, including the ACT and SAT. Getting a high score on these tests can help you get into a university with a 3.0 GPA.
Find out if any of the universities you want to apply to have special programs in place for students with lower GPAs, such as a 3.0. These programs give students who did not apply themselves in high school a chance to attend the university and prove themselves.
Attend a community college for a year or two before transferring to the university of your choice if you cannot get in with your current 3.0 GPA. Keep your grades up at the community college, and you will be able to use that GPA, rather than the 3.0 you earned in high school, to apply and be admitted into a university.