I've made many flyer's for both color copier reproduction as private party mailers, offset printed flyer's for large product campaigns, tear sheets for special product sales, magazine insert flyer's, and ads for the Thomas Register.
The one thing any good flyer should do is announce the product or event, give the times and place to see or attend, and offer contact information, the rest is merely pretty graphics that hopefully grab your intended audiences attention so they read what it is your trying to say or announce. Also a major factor is an easy to read font that portrays the essence of your endeavor. The one thing that all too often turns a good flyer into garbage is the over usage of different font faces which render it hard to read. Some would say that too many color changes also is a no no, but that all depends upon your focus, for a business applications, yes that would be rather unprofessional, but for a special event that is announcing games, food, contests and such then color plays into the formulation of a fun time.