Last week the Inblog at the Princeton Review started a series of posts on ACT test strategies. There are two posts over there already and I strongly recommend that everyone thinking about taking the ACT head over there to see the recommended strategies.
The first post was on what they call ACT triage. Basically, these are suggestions for making sure that you complete as much of the ACT as efficiently as possible.
The second post discusses the process of elimination and guessing. This post discusses why you should never leave a question unanswered on the ACT and shows you how to intelligently guess your way to a higher score.
If you have taken a Princeton Review prep course these techniques should not be new to you. But, if you are working on self prep for the ACT, there is some great information in these posts.