Nothing is more unprofessional than spelling and capitalization errors. If spelling is not your strong suit, consult a spell checker, dictionary, or at least a friend. This is particularly important if you are working with a language which is not your native one. Use title capitalization in all places except where full sentences are used. This means that all "important" words and the last word in a phrase -- regardless of importance -- are capitalized. Prepositions, definite articles, and conjunctions (as, for, to, the, and, etc.) are generally not capitalized except when they are the first or last word in the phrase, such as in "Save As...".