FWIW I started out running properly for the first time in September 2014. I've been playing 5-a-side football twice a week for 15+ years, and doing regular cycle commuting and Audax but I was far from running fit.
5-a-side football is good for CV fitness, but doesn't really do anything for straight line running. Stop/start/run/jog/walk/spring/walk/run/jog/etc for 60 minutes doesn't prepare you at all for an hour of steady running. In an hour of 5-a-side I'll probably cover 3-4km (depends on the size of the pitch and whether I needed to do my share of being in goal) which is way less than average walking speed overall.
Anyway, I had a gait check at the physio as I had broken my hip when I was only 2 years old and wanted to make sure I wasn't going to do myself damage. The physio also recommended the type of shoes I needed based on arches/pronation/etc and off I went.
He recommended to start off with 2 x 20 minute jogs a week (based on existing fitness from 5-a-side) and build up to 2 x 30 minute jogs adding no more than 10% (duration[1]) a week. When I reached 2 x 30 minute I should switch to 3 x 20 minute, and then maximum 10% increase again until I was running 3 x 1h a week. Speed or distance wasn't a concern at this point (I was doing most of my runs at about 10kph), it was just total duration and mostly done at the easier scale of things to minimise disinterest although I found my speed naturally increasing as I was getting fitter (and losing weight).
Given the 30 minute runs were typically 5k I moved one of my runs to Saturday morning to take in parkrun, and that helped give me a good speed workout and made me push myself faster than I would be able to do running on my own.
Stretching after a run is definitely a must; cyclists are generally very inflexible. Core strength exercises will help avoid many of the back/joint issues that new runners tend to be troubled by.
From there my running has taken off nicely, probably beyond what is relevant for a novice running thread. I'm still too heavy (weight down to 83kg but then back up to 92kg) but I don't seem to be having any problems because of this. Getting my weight down (and keeping it there) needs to be my priority, especially if I want to enjoy my running more and go faster. Extra weight takes its toll progressively more on longer runs.
1. I think my duration increase went something along the lines of: 20, 22, 24, 26, 28, 30, 33, 36, 39, 42, 46, 50, 55, 60.