What is the difference between the SAT and the ACT?

What is the difference between the SAT and the ACT?
I am very familiar with the SAT and have taken it twice, but now I am having to take the ACT and know nothing about it. How does it compare to the SAT? What is different? What skills do I need to develop before taking it?

The ACT has five different section types: Math, English, Reading, Science, and Writing. The math section only has multiple-choice. The reading section does not specifically test vocabulary. The science section is actually a lot like the reading section, only it also tests your ability to read charts, graphs, and diagrams in conjunction with the passage. The writing section is a timed essay on a topic relevant to high schoolers (like “dress codes”) and does not count as part of your overall numerical score. However, the essay does count as part of your Reading/writing score, and is sent to colleges as part of your score report. Some schools don’t even look at the ACT essay, and some place a lot of importance on it. Wrong answers are not penalized, so never leave a question blank even if you have to guess!

Also, check out this comparison chart for more details:

Kaplan also runs free practice tests and seminars all the time – if you attend one, there will probably be an ACT instructor running it and you can ask them for some advice, as well. Check their website for dates.