1. What are you trying to say?
Decide on your central message. Say precisely that, and cut out the rest. As you add text to your flyer, continue to ask yourself if that particular item is essential to supporting your idea. Many times, the job of your flyer is to spark interest and direct your audience to seek out further information. Can you get their attention and then direct them to call, email, or visit a website? Yes, yes you can. You don't have to answer every question that may come up on the one flyer. You need only give the pertinent facts, share an idea, and encourage the audience to dig deeper. If this is an event, the typical "who what when where" could be addressed. Ensure the very pertinent content is there, such as contact info, and move on.
"Your goal then should be to pare down all of the necessary information into easily-digestible chunks. Throw out anything that you don’t really need and look for ways to make what you do need more concise." -Joshua Johnson, "How to Design an Awesome Flyer (Even if You're Not a Designer)", Design Shack
As you continue to weed through the information, continue to ask yourself "Is this essential to the one thing I am trying to say?" If yes, keep it. If no, it's out. The remaining information should be clear, concise, and necessary.
2. Decide on a specific, painfully simple, concept.
When it comes to a concept, the good news is that there really is nothing new under the sun. You do not need to invent a whole new concept for flyer layout each time you sit down to announce an event. Browse around online for layouts that others have used, and adapt the appropriate one for your purpose. I'm a strong believer in those little napkin sketch diagrams for organizing your thoughts. Perhaps you can sketch out two ideas that might work, and then give them a try.