Lately I’ve been running doubles on Thursdays. Doing doubles is about the easiest way for me to increase my mileage. It would probably be easier to add more days of running (I currently run 5 days per week) but for now I’m sticking with doubles once a week.
Last week I was wondering if I was stupid to do a hard workout after only 3 hours of rest between my last run. According to this I did the right thing.