As a professional graphic designer for 40 years...yes before computers, I have to look away every day at some of the flyers I see online in social media. There is NO design. NO flow. NO professionalism. If you want to market yourself, you should represent yourself and your business as a professional and not with an attitude of, "Yeah, my kid could do that". And yes they probably can but it will also look like it unless they have a degree in graphic design. I have paid my dues and done my time. And as a friend of mine, who shall remain nameless (Patti) and I say, DAM@%# IT, I'm a professional.
Check out some BAD FLYER DESIGNS
This article pretty much covers most of the common mistakes made in design so you won't make them.
This is one of my favs! I would get into trouble if I posted some of the ones I see in my neck of the woods.