Hi thanks for your question!

According to the Radio Advertising Bureau to write great copy for radio you need to:
1. Find out what the client wants
2. Ask the client what's biggest thing they would like to feature, what is their demographic and what do their existing customers like about them. Make sure you take notice of what their image for their brand is, their business statements and their overall image. 
3. Once you have all of that, check out your clients competition and compare your client to them. Make sure in your ad copy you define the difference of your client to competitors 
4. Now you have all the research combine it all together to create a positve ad copy for your client. Make sure the copy is straightforward and contains an active voice and a call to action
5. Consider if music and sound effects are appropriate
6. Consider if you want to add a real life element, like a conversational style ad
7. Work out if humour can be applied in a appropriate context
8. Write for conversational pace and read it aloud several times. 

And there you have it. 
Hope this helps.... Happy writing!