For a beginner, I'd suggest just putting up the rides that come already constructed, and study them! Watch how they run, see how the elements are put together, and watch the speeds they have when they hit those elements. Then start with a steel mini coaster, it's one of the easiest to build and work with. Get used to that, and you'll be well on your way!
Also, make sure your coasters aren't going too fast into unbanked turns as well as inversions. Wrap the coaster around itself to help your excitement rating, and don't underestimate the value of putting trees and paths around it. Enjoy!
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Po!nt of View: A different look at Roller Coasters.
http://www.crosswinds.net/~justmayntz/thrills/index.html