FightingIrish posted a good link to real self defense law and procedure by Marc macyoung I believe.
What alot of people consider self defense, ie your typical barfight, will get you arrested for assault and battery. Its not worth it.
A few weeks ago I was out in one of our main drags for bars here in Pgh. Every single time ....someone tries to pick a fight with my friend or I. And believe me, I am the easiest going guy ever. So I am walking back to my car with my friend, whom I train with and of course some drunk buffoon is out on his porch and starts calling us out for whatever reason.
He brings his friend out who insists "he isnt giong to get involved, but that drunk friend will beat both of our asses and he will put it on youtube". Of course my pride made me wanna tool this guy, and between two trained fighters...it probably wouldnt have been to difficult. But...he made no move to attack us, didnt insult any girls we were with... I said "you win buddy, youre the tough guy" and drove away. Beats the possible legal ramifications that would occurr.
If you want to learn self defense...do so....but you arent gonna learn stuff from books or videos. If you do get into a fight, it should really only be a life or death situation...so i would suggest carrying pepper spray, a knife, or a gun...and using them only if you have to. Otherwise ALWAYS walk away.