Discretion is the better part of valor.

You had better take your umbrella in case.

Much caution does no harm.

Take care.

Beware of one who praises you to your face.

He is shy of telling the truth.

He advised caution.

On the way out I said to my waitress, "Be careful, Sue. There's something funny about the glasses you gave me - they're filled in on the top, and there's a hole on the bottom!"

Do watch your step.

Guard against accidents.

I was wary of showing my intention.

I was wary of showing my intentions.

Look out for pickpockets on crowded trains.

We should guard against traffic accidents.

Guard against the danger of fire.

Be on your guard against fire.

Keep on the watch for anything to come.

Not being watchful, the driver failed to stop in time.

Take your coat in case it rains.

You should be on your guard when doing business with strangers.