Obviously each event will be different. A larger event with a lot of people will be different to organize than a small MozzCoffee. We would suggest that you ask for advice from your mentor or other reps in your area. Or look for a rep that organized a similar event to the one you would like to carry out!
However, there are general guidelines that you can follow. You can find links to more detailed instructions for different events here and more tips here.
As a general tip, a successful initiative will need up-to-date content that is going to be interesting to your audience.
On-line events: Remember that you can always organize an on-line event. It is not necessary for an event to be in-person. Just ask yourself what would be more productive and cost-effective (and, more importantly, safe) for the event you have in mind.