Be polite. And a tip, don't go mushy gushy in front of her the first few times until you guys are VERY comfortable around each other. :P Also, try not to be too stiff. Act "normal"? I should say. Laugh a little, let lose, but don't forget that you're trying to make a good impression! Good luck! :)
In these cases, it's just best to be yourself. Do not try to put on act as this may place you in low standing. You should also realize that your boyfriends mother does not get to determine whether you two remain together.
Smile, friendly, have fun. No fake. Try to relax. She is probably a little nervous to meet you too. Ask your boyfriend about some of her interests and start a conversation. Ask a couple questions. You will be fine. Smile.
Wear nice clothes , nothing that hikes above the knee too far . and your neckline should be comfortable close to your neck . smile , don't be too nice . Talk only when you are spoken too . Don't drink any alcohol . Ugh !!! Good luck !
wear something pretty nice but that you are comfortable in. it'll help you relax if you don't have to worry about your clothes. make a good impression by being yourself,she is going to know you anyway,so why not let her see how nice and confident you are. make the best of yourself show. be complimentry,but not too much. just keep in mind," balance in everything". that ought to do it. have fun,that is a form of a compliment too. shows that she is seen as a person that others are at ease around. oh yeah,one more thing. not too much kissy kissy around her. good luck......