Sometimes I come across a term in English, my target language and I work back to what it would mean in Spanish, my source language. Take the word "felony". My initial attempt may come out as a direct translation that does not reflect the true meaning of the concept, but with a little research, I hit on the right answer.
Many times I need to flesh out what the English term itself means (as in, what is the difference between a misdemeanor and a felony?, how is it used in a sentence? Who has been accused or sentenced for a felony?). To do this, I "reach" for online thesauri as well as a site called Wordnik and Google searches as well. I also look up the term in an English-Spanish dictionary. Then I look up the most suitable Spanish definition in a Spanish monolingual dictionary such as the Diccionario de la Real Academia de la Lengua Española.
The clearer the picture, the better, and the better equipped I will be when I encounter the Spanish term (delito mayor, crimen) in a Spanish document I am translating.