Dear XX:
I'm wang Lin,I write this letter is to want to invite you to XX evening party.If you could come,we will be very happy.
This party is for (content).The party will begin (specific time and place).First of all,(schedule a),then (schedule ii).
I know you very busy recently,so I hope you can in spite of being very busy toglance take time to attend.No matter whether you can come,please give me a reply as soon as possible,so that we can get ready.