Congrats on returning to school. I started out on a rough patch also. I returned to school after a lengthy absence with a 2.1 GPA and have significantly brought it back up since then! If your science and mathematics skills have been neglected for years you will be glad that you refreshed before tackling the classes head on! I restarted college with College Algebra at first and then began taking the classes I need toward my associates degree. I'm now going to start working on my bachelors in January at Uni.
Try Khanacademy for math and science, Patrick JMT on youtube for mathematics, ratemyprofessor dot com to find reviews of professors and instructors from students, and look on Amazon for study guides for the areas you will need a refresher in. Amazon has customer reviews and testimonials that are very helpful for the books that are on sale on Amazon.
I wish you the best!