The LaTeX guide on the Art of Problem Solving website would be very useful:
http://www.artofproblemsolving.com/Wiki ... TeX:BasicsIf you have questions about LaTeX, we would be glad to answer them.
What grade are you in?
Also, as for the "reasonable scores" question, it depends on several factors, such as your grade (seniors should do better than freshmen), your coursework (e.g. taken Calculus as opposed to taking Geometry), your school, and independent study. For a complete beginner, just making a positive score might be something to be happy about (especially for Number Sense, where many people do very badly to start.) If you don't reach the 100-150-150-150 threshold, don't worry. It comes with time, and eventually, with practice (unless you're a senior and have very little time) you have the potential to reach scores in the range of 350-300-300-300 (which is quite impressive, although beatable by the very best.)
If you have questions (and you will,) feel free to ask in the proper place on the forum. There are many things that you should know on these tests, that are very difficult to figure out independently. For example, there are many "tricks" or "shortcuts" on Number Sense, and in Calculator, a TI-89 and HP-32/33 is what you should aim for for your two calculators. Science is mainly self-explanatory.
Here is the Academics home UIL website:
http://www.uiltexas.org/academicsLook at what is said for each contest in the "Academic Contests" tab.
Good luck!