1. I do not think this can be stressed too much: do not reread your applications once you have submitted them. You will notice all of the flaws in them that somehow you missed before pressing the submit button. All this will do is lead to weeks of agony as you wait to hear back from all the schools you are sure will now reject you.
2. Mistakes, even in a SOP, are not the end of the world. If you come off as a strong candidate with clear goals, drive, and ambition schools will not necessarily reject your application just because you made a typo or two.
3. Do not apply to somewhere you would not want to go to if you got in. If you would hesitate to go somewhere, even if it is your one acceptance, it is not worth applying to.
4. Do not apply somewhere that does not fit your interests, even if it is a top ranked school. You may have stellar credentials, but if you do not actually fit into the department, chances are you will not get in. All you are doing by applying is wasting time and money.
5. When trying to figure out where to apply to, start by identifying what it is you want to study. Then try to find which schools have professors with similar research interests. Talk to your adviser about your interests and life goals, and see if he or she can offer up any programs to look into.