It's easy, get a few forum friends, discuss the idea, promote the idea and have friends participate in promoting. Next thing you know you got a crew of people interested in the game night. Also I would suggest having a fixed time for said event so that participants know when the event starts.
Here are some suggestions I would give:
1. Promote - Announce that you are doing this. Try to gather and accept feedback from others and implement as much as you can.
2. Accessability - Not everyone can play at the same time, due to time zones and everyone has their own lives. Choose a time tat fits for everyone. Example: 9 pm EST can make it possilbe for many people to play since it'll be 6 pm Pacific in California. But it might be hard for those in the EU.
3. Game - Pick a common game that everyone would be interested in an set it up in a way that people would want it. Example: Many people play Starhawk and Pilgrim sets it up in a way that many people like it. I set my event in the All Stars forums up with rules and manner that everyone wants.
4. Keep it fresh and consistant - If the game you choose has a variety of modes, use them if everyone agrees. If you are doing this every week, try to keep it the same time every week, unless you have other plans.
5. Feedback - Listen to everyone. You may host it. But people will participate and would like their voice heard.If people don't like how something goes or doesn't agree, discuss and compromise.
6. Fun - Have fun and keep it fun.
Ossie gave you some very solid advice. I have a lot of experience hosting community game nights myself. This is what you need to do, step by step.
1) Create the thread for the game night. In the first post state the date(s), time, and timezone. If the game has DLC content specify if it will be needed.
2) Guage interest. Ask people interested to sign up, make a list, once you hit your pre-determined "enough to have a good event" number you can then move forward and make it more official.
3) Making it more official. If you get something together and want some extra attention for the thread and event send me a PM message here on the forum. I will try and get you on the weekly calendar and try and have someone promote your event over on the social media sites via the MVP program.
Check out a few of my event night threads if you want ideas. MAG Thursdays, Warhawk Wednesdays, Starhawk Wednesdays