Here are some horrible truths:
Most radio drama is very badly written. Radio drama is an endangered species. It has never taken a hold of mainstream programming on commercial radio in the UK. It used to be the mainstream in the States and Australia but lost out to TV in the middle to late fifties.
It is under threat within public radio services including the BBC because of the pressure of monetarist ideology and the fact that authors and radio drama directors have been too complacent. IRDP is a significant oasis and continues to support the principle of the original play.
Ground rules
The Beginning
The beginning is everything. If this part of it does not work you are 'up shit creek without a paddle'. Your listeners will desert you. You have failed. You do not exist as a dramatist. Booo!
The Moment of Arrival
This is how you drop your listeners into the story. Don't give them a warm bed with comfortable pillows and a hot water bottle. The background and sub-text of previous histories is better explored through revelation in dramatic action. So parachute your listener into a top dramatic moment. Not the climax. That would be premature. Find the MOMENT to join the story. Avoid the slow snail's explicatory route. Kick 'em into a high energy trip and whoosh them through the rapids.
Structure
Set up...struggle...resolution. You can reverse this if the set-up is more dramatic and explosive than the resolution. Regard your play as a series of phases
The Plot
This is the story with lots of twists and turns. The more the merrier. Most listeners like good exciting plots. Without a good plot you're eating a souffle that has gone flat. You need plot, more plot and more plot. Run at least two story lines. Two sub plots would be interesting. Keep the plots linked logically within the same play. The best system is a major and a minor storyline linked to one another. Get them to come together at the end.
Surprise
People are hungry for