I need some help as you see I want to know?

How do I get better at verbally standing up and standing up for myself properly for myself?As I don't do it enough and let people get away with comments and snide remarks to me and rude people have started arguments with me in the past and I have not said anything baCK TO THEM.I am a nice person and just look to get on with everyone but sometimes in Life I have come across rude people like one time when me and my friends were going into a club and a bouncer said some comments to us, I said nothing back but my friend stood up for himself - how do I get better at standing up for myself?As it just doesn't seem right and logical to take things off of people when I don't do anything to anyone just keep myself to myself and mind my own!!!It happened again earlier today as I was just dragged up by a person on the streets who followed me onto the bus and made a complete FOOL out of me {my brother's Friend DK would have been ashamed of me as he would have been thinking why I let someone practically bully me so easily as if it was him he would have knocked the person out with one Punch}, I need to get better at "CONFRONTATIONS" - I WANT TO GET PAST THINKING IT IN MY HEAD, STOP HESITATING AND JUST DO IT!!!As have been taken advantage of in my old place of employment by my managers and other employees who I worked with!!!