Some languages can help to learn some other languages but this happens when the languages are similar. English is an odd language -- it's not very similar to any other. If you're good at Portuguese, Norwegian, Russian or Polish, you will find it easy to learn Spanish, Swedish, Ukrainian or Czech respectively. English doesn't have anything as close to it.
However, learning any European Indo-European language will give you a better start to (preposition chosen based on a quick glimpse at google results and intuition) learning another one. There's a large number of words common to all of them and even more common to some. We have all taken a lot from Latin and Greek, and then from Italian, French and English.
Also, English is quite helpful in learning other Germanic languages. No one had to tell me what "Hilfe" meant in German when I saw it for the first time because I knew the English word.