You were promoted recently. And you want to invite your friend Jack for celebration.
Write a letter to Jack. In your letter
1) describe why an when you want Jack to come
2) tell Jack what to bring with
I am pleased to invite you to join our little celebration which is currently planned to be held on Feb 23rd. so far we have not yet decided the precise time, but there are a collection of choices about locations, which I want your suggestions, including my office, my home or anywhere you consider convenient.
Your earliest response will be highly appreciated, and I will definitely take into consideration all suggestions from you or anybody else being invited, before reaching the final decision.
The celebration is mainly concerned with my latest promotion. Without your thorough support, and my other friends and colleagues, it is impossible for me to be promoted, as I have been merely working for the company for half a year. Meanwhile, I feel it a precious chance for us, a group of friends, to come together to hold a relaxing talk and have some delicious food.
Please do not bring anything but yourself if you can come over. If you can add some amusements to the celebration, for example, some jokes, I will be greatly pleased. I am looking forward to your reply, and waiting to meet you.