I have been in this situation many times
Firstly set yourself a goal, which should be realistic, Ideally a race in the future.
The distance and severity, depends on your capability before you were injured.
OR as I do set many goals of races of increasing distance and severity, ramping up to where I want to be for my ultimate goal.
As you will have heared many times, do it slowly! Your mind may be capable of running a marathon, but dont expect your body to adapt overnight to this punishing treatment. You will end up injured again.
The general rule is increasing by distance 10% per week. Although I sometimes exceed this myself.
Start by running half what you think you can do.
As well as starting with less distance start with less speed, run a few times before ramping up the effort, again do this gradually.Any signs of pain then ease off - it should be enjoyable- not painful.
If you need incentives to go out and do this the races looming will help, but joining a running club will also assist later, however -dont get carried away and try and keep up with the big boys, run at the back of the group.
Follow these rules and you should have sucess and enjoyment.