E.g. I decided to forgo the chocolate mousse and just ordered a coffee.
As explained in the foregoing paragraph, there are two aspects to be considered...
It was a foregone conclusion that Barry would forgo his wedding and head off for Thailand with his mates.
Udo is basically right, and it definitely needs to be pointed out that "vorangehen" is the primary meaning of "forego". (Usually used as in the above examples, as "foregoing" (adj.) and "a foregone conclusion".)
The fact that "forego" has also come to be a variant of "forgo" - the latter being the originally correct word for "verzichten" - results, no doubt, from years of people confusing the spelling.
The clue lies in the prefix "fore-" meaning preceding in time (Ger. "vor-") (as in before, foresee) as opposed to "for-" (such as the prefix in forsake, forgive etc.), possibly comparable with the German "ver-".