The tip I learned and passed on to my (then) teenage children is:

Spit as hard as you can straight into the attacker's face. This gives you a second or two of blindness, since EVERYBODY blinks when spat at.

Perform the aforementioned kick.

Remember that if your adversary gets up quickly, he is going to be very mad.

Run like hell and make noise.

But the best advice of all is do your utmost never to get into such a situation.