On Friday, I want you to run for at least 60 minutes. If you can go longer, go for it. Not fast, but at decent conversational pace. Then, Saturday, add twenty minutes to whatever you ran on Friday, and run at the same pace for that amount of time.
For example, if you run 65 minutes on Friday, run 85 minutes on Saturday. Simple, huh?
In all cases, Sunday is an active rest day.
Now, don't shirk on Friday to make Saturday easier. Running is about stress, adaptation and recovery. If you don't push yourself, you'll never get any better!