I don’t know anything about USC, so I can’t tell you.
For UC’s - The main things UC’s care about are GPA, completed prerequisites for your major, at least 60 units attained before you transfer, and the completion of general education. Do your best to get as high a GPA as possible. I’d say have a 3.8+ to be competitive, but just do the best you can, and of course, the higher the better. A friend of mine got into UCB’s Political Science major as a transfer with a 3.5 (but an upward trend) and minimal extracurriculars.
For general ed, just follow your school’s IGETC pattern, and take whatever courses you find interesting to satisfy them. Finish your math and english requirements as soon as possible, at least by the fall of next year. Honestly, the sooner you get these courses out of the way, the better. IGETC is around 39 semester units, I believe? Once you finish that, you can take whatever you wish to get to the 60 unit minimum. Make sure you take UC transferable courses - they generally say they’re transferable on course descriptions, but most standard courses (3+ units) are.
Regarding major prerequisites (the courses you need to be admitted into the political science major at a college you’re admitted to), check assist.org. It looks like your college has most of the courses you need to transfer, but you’ll probably have to take some at a UC. Don’t worry if some courses are not articulated - they won’t count it against you. If you want to take every single class, you might be able to find the course you need at a neighboring community college, but if you go to another school, make sure you take all the classes you need. You can attend multiple community colleges at once, it’s not a problem.
Here’s your school’s IGETC pattern - just follow that, and make sure you have it finished as soon as you can. By Fall 2016 is preferable, but plenty of people complete it in the spring before they transfer. Some AP units from AP tests satisfy IGETC courses and give you units, as well. Talk to a counselor about this as soon as you can. http://www.citruscollege.edu/stdntsrv/counsel/articulation/Documents/IGETC/IGETC2014-15.pdf
Here’s assist. This is an extremely important resource. Check it out, and compare transfer agreements with your school and other UC’s/schools. It has tons of information, and is seriously helpful. http://assist.org/
Use ratemyprofessor.org/ to look at reviews for teachers you may take. It makes a difference, and is REALLY useful. Look for your school’s course schedule (it’s probably online, but I’m sure they have a physical copy at your school) to see which courses you want to take and whatnot.
Other advice - plan everything in advance. I wouldn’t take more than 12-13 units your first semester - a sample schedule would be something like:
POLI 104 - Intro to Political Science
ENGL 101 - Reading and Comp
MATH 165 - Introductory Statistics
ANTH 212 - Physical Anthropology
You can take whatever you want, though. Honors courses are good if you want to be challenged more, but I don’t think they’re absolutely necessary. If you want advice about fun classes to take, I can tell you, but it’s mostly up to you to see what you’re interested in. All of those courses satisfy IGETC areas. Try to take classes at times that work best for you, get involved in some clubs, and try to meet people for study groups / as friends, if you wish.
Regarding textbooks, I’m not exactly certain. Sometimes professors post the textbook you need on the course information (kind of vague, I know). You don’t necessarily need it ahead of time. I recommend researching the material (you can watch lectures of different classes online if you’d like, or you can search up what a course involves, etc. - google is a wonderful thing) before the term, but it isn’t necessary. You won’t be expected to have your textbook by the first day of school. All of that will be explained in the syllabi your teachers give you.
I think you’ll have to take math/english placement tests before you can choose your classes, as well… Talk to a counselor at your school about that, or anything else you need to do before the term starts. Counselors are also good for helping you make a plan to transfer, and can help you plan everything out ahead of time.