Hi Ferran and welcome to Discuss Fitness.
I have found and used some great running training plans at
RUNNER'S WORLD MAGAZINE. If you haven't been there yet, check it out.
I ran a half marathon once, many moons ago. Now I run shorter distances, nothing further than a 10k. I am prefering even shorter distances like the 2-mile fun run I participated in on New Year's Eve. I also did some track distances during the summer, from 100 meters all the way up to 3,200 meters.
I'm not sure how the running fits into the bigger picture of your fitness goals. For me, I have found that shorter distances run pedal to the metal have contributed more to my fitness growth than when I was focusing on the longer distances.
Have a great day!