Your next date with your present boyfriend is going to include his friends and you are about to have a nervous breakdown. You want to impress them!!!
Your partner is one of those people who has really good friends, they have been there for him since for ever, in good and bad times, and provide him with advice in other words they are like his family. Once you realized the importance of their friendship you want to make a good impression. Trying not to lose your sanity while thinking about your outfit for tonight, the topics to talk about, if give or not your opinion in fact, you are not trying to impress him anymore, you are trying to impress them and be judged by the hardest of all judges… his FRIENDS!
My advice, be yourself. If you try to become someone you are not everyone will know you are faking, specially him and it will make things even worse so do not be afraid of who you are. Do not forget your outfit, that is important too.
If there will be women as well you have to show them you are a modern and elegant woman with good taste. Of course all depends of where are you going to choose your clothes and make up. Women like other women as friends who are fashionable, free and know what they want on the other hand if this is boys only you need to be and fun and sexy, but always within your limits and good taste.