Cuando veas a tu vecino las barbas quemar pon las tuyas a remojar

[ROBINDESBOIS]

English?
'

[Rusty]

Literal translation: When you see your neighbor's beard burning, soak your own.

I'm not familiar with this saying. Taken at face value, it seems to warn of impending danger and doing something about it before one falls prey.
I can't think of an equivalent saying, yet.

[AngelicaDeAlquezar]

The idioms section has a proposal (http://www.tomisimo.org/idioms/es/cuando-las-barbas-de-tu-vecino-veas-pelar-echa-5186.html)...

[aleCcowaN]

The idioms section has a proposal (http://www.tomisimo.org/idioms/es/cuando-las-barbas-de-tu-vecino-veas-pelar-echa-5186.html)...
That's quite right. The saying including "quemar/arder" is a variation used by people in Spain and maybe giving a different meaning ("be prepared because you're next!"? "it may happen to you too"?) to the traditional proverb "cuando veas las barbas de tu vecino pelar/afeitar/rasurar/cortar, por las tuyas a remojar/al remojo/en remojo" that is "you should learn from other people mistakes". The phrase "poner las barbas en remojo" ("to learn one's lesson by the mistakes made by others" specially when one yields after having resisted) comes from that saying.

[Rusty]

'(You should) learn from other people's mistakes' fits very well, then.

[sosia]

I think "arder" has no really meaning here.
I always though it refers to the medieval ages, when havin a good big beard was a sign of autority and adulthood. When someone was powerfull enough to cut other's beard, it was good to soak your own and make the thign more easy (and less painful :D )
Here there is a very good reference (but with other meaning)
reference here:
http://www.finlay-online.com/albarranschoolofmedicine/espanolconozca6.htm
So the usual version it's the one aleccowan has given, and the other a misunderstanding --> You must soak your beard in order not to be burn.
Saludos :D