well, never trained for shorter distances, done marathon 5 times with a PB of 3:10, but only once did I break 20 minutes for 5K (around 19:30) all the rest have been around 20:30, and I am really fed up (maybe I have raced 5K 8 times so far).
I am just coming back from a local 5*5 relay race, I was in two teams, 2nd runner in the first team and 5th runner in the second team (about 45 minutes of rest in between), my times were 20:30 and 20:45, and after finishing both races and about 1 minute of rest, I was completely fresh, so it seems I just have to learn how to push myself...
So I have decided to train for a 5K. I can put 2-3 month of training into it, and my plan is to go sub 18:30, is that doable?... any suggestion on the training and if possible, links for free online programs?