Struggling

I am really having a hard time knowing how to deal with the limit testing of my 3-year old.  He wants to do what he wants to do when he wants to do it, and he is very stubborn about it.  Sometimes it can just seem silly, but it can get to the point where it is dangerous.  I don't want to get overly angry at him or label him -- or let him be labeled -- as bad.  How do I love him through this, and help him grow up to be an independent person who als does have consideration for people around him and respect where it is due?