Having worked as a foreign-language technical translator for 25+ years (Spanish, French, Russian), my advice is to read as much as you can on a variety of subjects in both your native language and the language(s) you plan on translating into, plus being thoroughly versed in their grammars, plus being flexible in your thought processes. Two cardinal rules: 1. translate ideas, not words, and 2. aim at being impossible to misunderstand.