It's took me a long time to reach the point in which i can manage 5k in 30 mins (well almost). I was a slow coach runner, i think i even graduated at something like 7.5/8kph.
I managed today's result by making a variation of the c25k+ speed podcast.
I did my five minute walk, and then a five minute run at 9.5kph, i moved into the six interval runs, bumping up to 11kph for the minute, and then dropping down to 9.5k for the slower speed. Repeated as the podcast said, six times.
At the end of this though, instead of slowing down, i ran another five minutes at 9.5kph, reset the podcast back to the beginning of the intervals, and ran a further three intervals at the same speeds as before, and finished off the 5k back down at 9.5kph.
So in summary, 21min 15 sec @ 9.5k and 9min @ 11kph.