Honey, I didn't know which colleges I was applying to until December of Senior Year, and I finished my applications the DAY OF the deadline.
11 applications, 0 rejections.
It's not that bad.
You really don't need to freak out, at all.
I didn't apply ANYWHERE early decision. Early decision means that your application is due early- usually November of Senior Year. You'll usually find out in December if you were A accepted, B waitlisted, or C rejected. Early Decision means that you are committing to that school- it is your number one choice school, and if they accept you, you HAVE to go there. Therefore, you can only apply to one school early decision.
The second option that some schools offer is Early Action. It's the same as Early Decision, but non binding- if they accept you, you can still choose to go to a different school.
Early Decision and Early Action applications usually give the applicant a slight edge over the Regular Decision pool. However, they only see the first quarter of your senior year, and you don't have a lot of time to involve yourself (extra curriculars) senior year before your app is due. They WILL check your grades mid year, and at the end of the year- if your grades slip significantly, they may put you on academic probation, or even revoke your admission. SENIORITIS=BAD.
EA and ED also means you need to get all of your testing done early. Your basic tests are the SAT, ACT, and two to four SAT IIs in various subject areas, in addition to any AP exams you may have taken. Not all colleges require SAT II subject tests, especially if you submit ACT scores, but if you take one and do really well, they'll definitely help you. Of course, all of this costs money, so test wisely, and find out what tests your colleges want.
DO NOT FREAK OUT AND TAKE THE SAT FOUR OR FIVE OR SIX TIMES. It's not worth it. I took it once- that's all anyone needs! Don't waste your money on expensive prep courses, either- waste of time. If you want, get a book and work with it on your own, but in general, just look at the practice questions on the College Board website. If you're shaky with grammar, grab a copy of
The Elements of Style and make it your bible. Admissions committees are sick and tired of seeing students for whom test taking has become an EC.
Now, the common app. The VAST majority of colleges use the common app- it is your friend. Of my 11 schools, only 2 weren't on the common app. You fill it out ONCE instead of, say, 11 times, and submit it to all your colleges at once. Very often colleges will have their own supplement to the common app, where they might ask you some short answer questions or an additional essay. The common app site is CRAZY helpful because it outlines what you've done, what you still have to do, when your deadlines are, etc. It's a beautiful thing.
Application fees: these run, in my experience, from as little to $30 to as much as $70. Throw in money for sending test scores, money for taking tests... it all gets really pricey, really fast. If you come from a low income family, sometimes the college will waive the application fee- check this all out beforehand.
Um... I think that's a decent overview. Let me know any specific questions
GREAT college research sites:
www.collegeboard.com (make an account here if you haven't already- these people run the SAT and AP exams)
http://www.princetonreview.com/home.asp
http://www.collegeconfidential.com/ (use this one SPARINGLY. it is FULL of obsessive prestige hungry resume stackers- I went here a lot, and was convinced that no colleges would accept me because of it. These people are not the end all be all [I'm referring mostly to their forums here]! They can be helpful, though, so don't be afraid to ask questions.)
Um, yeah. There ya go. I don't know anything about California schools, all the ones I applied to are on the east coast. Sorry.

L'amour est un oiseau rebelle.