Avoid too much PDA --Public displays of affection should be kept to perhaps holding hands or just resting your arm on your significant other.
Avoid getting trashed— Don’t drink at all or limit yourself to one drink before dinner and then only one after. Keeping your wits about you will help you pick-up on the cues some family members maybe trying to send you about your potential future.
Avoid views on politics and you have never had sex. At least as far as your SO’s family is concerned. They may not share the same feelings you and your sweetie share and they certainly don’t want to be thinking about their family member having intercourse.
Don’t lie/exaggerate about yourself—May seem harmless puffing up yourself to look good in their eyes. But in the end if the relationship lasts they will know you better and they may consider you a phony from that day forward.
Don’t be glued to your phone! –Nothing says, “I don’t want to be here” like being glued to your phone.
Don’t tell any jokes—Again as far as they are concerned you smile and laugh at what they are saying (if it is funny) but you don’t spring any of your jokes on them because at this beginning stage, of the relationship, you couldn’t know what topics would be deemed inappropriate.
Don’t be closed minded—Some holiday tradition they have may seem completely strange but by not knowing the background it may just be that you do not understand its importance.
Don’t sit around--Clean up! (Margie’s note: the first time I was invited to a serious boyfriend’s house, I let stress overwhelm me and didn’t offer to lift a finger. They never let me forget that. Thankfully that relationship didn’t work-out for other reasons! ) So after dinner don’t just sit there.
Don’t dress like a slob-Sure your SO says it is a casual gathering. You are not yet a casual acquaintance of these people. So you need to wear something a bit more presentable then comfy.
Don’t talk all about you but do talk only about you—Your SO’s family doesn’t need to know about all your family matters and they don’t need to know every detail of your life. Of course they will want to know you better in the same way your boss would. Meaning: be polite, follow the conversation and chime in where appropriate.