I'm a fan of the FIRST "Run less, run faster" programme. So, I've cobbled together a spreadsheet that does most of the heavy lifting in terms of working out the timings that one needs to do. Just change the yellow cell to reflect your 5K race pace (that you have/can actually-achieve).
For a brief(ish) summary of the programme, you can read the article at Runner's World.
FIRST actually have two programmes, one for a first-time marathoner, and one for the experienced runner. This spreadsheet is for the experienced runner …. despite the file title being FirstMarathon.
Finally, my friendly spreadsheet auditor has yet to cast his eyes over this, so use it at your own risk.