Online dictionary

One of the best to my mind is the following one:

www.wordreference.com

I above all advise it from English to French.

The tip I could be giving would be to check systematically from English to French, once you use it from French to English because misunderstandings are numerous if you don't do so.

It's also helpful because at the end of each page, you can have a view on a forum full of relevant information.