Meeting the parents (expecially his mother!) can be a very stressful task! The first impression says it all, and if you see a future with this one, you definetly want to make the BEST first impression! Follow the below steps and you should be in the clear!
This is the most important tip that anyone can ever tell you and I'm sure you all know this. Trying to hard will not get the parents to notice you, while you acting sincere and real will make them get to know you for you. Remember if you are wanting a future with this guy, acting fake can't last forever.
Try to find a common ground
If you know your boyfriend's mother is really into a brand, hobby or cooking, try and casually bring up a conversation regarding the topic. This will loosen the air and make everyone feel a bit more comfortable, also will show the family that you are genuinely interested in getting to know them.
At least for the first little bit! No matter what parents say, they do not like seeing their son (or daughter) being groped by their significant other. This can even sometimes seem like you are trying to over compensate for something! If this is one of the first times you are meeting the parents, don't make the air uncomfortable and weird. If you see a long term commitment with this guy, be gentle in public!
Wear something you are comfortable in, but since you want to make an impression, wear your best outfit! Obviously this is depending on what you are doing the first time you meet them, but dress appropriate. Keep your lady bits tucked away, and don't wear something you have to fidget in!
Be polite! Make sure to say that you are happy to meet them and thank you for everything they have done. If his mother is in the kitchen preparing the meal, ask if she would like some help. This will be your time to break the ice and chat her up!
Remember, if your meeting your boyfriends parents, there is a strong chance he is really into you!