Going to the ground is not your best choice, especially not when you have to engage multiple opponents. Also if there is a child or loved one with you that you need to protect, what do you suppose will happen to them while you are on the ground. Your best strategy is to incapacitate with a blow and only go to the ground if you have to.
If you are in a critical situation and it is apparent you are about to get hit, go ahead and hit them first and hit them hard. If you allow them to hit first, you make a bad situation worse and will have to recover from it to get back in the fight. If there is more than one adversary, it is imperative that you go on the attack. The only problem with this advice is that if it comes to court, the situation may be reversed and you end up being charged with assault.
Remember, in the street there are no rules, the goal is to be the last person standing and walk away unharmed if possible. Don't hold back and don't give up if you get hit. Do whatever you have to, bite, pull hair, gouge the eyes, whatever it takes to win. If the situation is life and death, go for rabbit punches to the back of the head and heel kicks to the spine, but remember these techniques will maim or kill, do not use them unless absolutely necessary.
Don't engage unless your life or safety is in danger. If they have a weapon and all they want is your wallet, give it to them. Going into a life or death confrontation is not worth the twenty bucks in your wallet and a few credit cards. Have the credit cards cancelled when you get home and write it off to fate.
Don't hurt anyone more than you absolutely have to. You're goal is to force them to leave you alone, not to punish them, overdo it and you're apt to wind up in court.
Remember your objective is not to win, it is to return to a state of peace. If you stun them, run away as fast as you can, people have lost their lives because they didn't have the good sense to run once they stunned someone.
Forget about what you see in the movies, stick to proven simple techniques, you're not out to sell tickets, your goal is to survive.