What to avoid:

Try not to show love (at least physically) too openly. This can make the partner's parents feel embarrassed. 

Stay away from controversial and personal topics like politics, religion, health, etc. Choose positive and engaging topics where everyone can say something. Some options: your childhood, your partner's, acquaintance, etc.

What to do:

As one of the "safe" topics we mentioned above, ask your partner's parents to tell you some funny stories from their boyfriend's childhood. Parents die talking about children!

Bringing a small gift is a good idea. You can ask your loved one to give you some ideas for a good gift for mom and dad. Such small gestures can leave a lasting impression.

Dress simply but well. Choose a comfortable outfit that can help you act natural and feel relaxed.

Ask your partner to tell you more about your parents. This will help you get the feeling that you know them even before you meet them physically.

Get ready to tell them more about your family, interests and passions.

Some compliments never do harm, but caution. Do not overdo it by leading it into servility. Be true to what you say. Evaluate home decor, food, how children have grown up, etc.

Most important: Be yourself. Do not try to pretend that you are someone else just to leave an impression. After all, this will not be the last time you meet, so the interest and presentation should be as sincere and genuine as possible. Enjoy the evening and do not forget that your "embarrassments" are also shared by your partner's parents. Make this experience as enjoyable as possible for both parties.

Ps: Congratulations on this step your relationship is taking! :)

Source: Life Hack, Bright Side