Your leaflet type is invariably determined by the cost of your product. The more expensive the product the more elaborate and finer quality will be the leaflet.
The size of the leaflet can matter to certain campaigns, but A5 and A6 are the most popular, followed by A4.
A new owner to a traditional Fish & Chip Shop may only really need a BLACK on WHITE leaflet, but a £15000 Conservatory ideally needs a full colour glossy leaflet.
Choosing the Content and Design
In general all leaflets should follow the AIDA formula --ATTRACT readers' attention, generate INTEREST in your product or service, create readers' DESIRE for what you are offering, then finally ask for ACTION.
Create a catchy heading, be precise with the rest of the content, include a couple of interesting photos or graphics, and finally ask for action. Tell the recipient what you want them to do or they simply won't do it.
Different Types of Distribution
Through letterboxes -- Solus distribution (delivered on its own), Shared distribution (delivered with other leaflets).
With SOLUS the leaflet is the only thing through the letterbox. SHARED is a cheaper option, but is delivered with other leaflets.