These are some tips based on my experience working at various radio stations. They probably won't guarantee airplay but will certainly make your chances that much higher. Feel free to add yours below.
1. If you submit your song to a radio station, never have it longer than 4mins 24 secs.
2. If your song is accepted and is between 3 - 3:30 mins, the higher the probability that it will get heavy rotation.
3. NEVER give the radio station the full album. Select a single, get a nice cover done and give it to all radio stations. - Most stations do not have the staff / time to listen to music submitted on a daily basis. Presentation is also key and will entice the producer to give it a chance.
4. NEVER give radio stations more than one single in a span of less than 2 months. If by chance your second song is also selected, it will compete with your first and kill it off (or both kill each other... the listeners will not have time to 'love' the single)
5. In general, most songs that start with the chorus end up being huge hits. e.g - Reason (Eko Dydda), Pages za Bible(Alemba & Sadic), Saluti(Daddy Owen)... the list is endless. On the chorus part, make it simple and if you can, repetitive.
6. Try make a radio version of your single and start it with the instrumental. Trust me, presenters love this. They can talk over your song and introduce it.
7. Call in or SMS to request your single. If you don't, who will?