I think the important thing to set yourself is time goals rather than distance. Regular running is key, and you'll soon find that running becomes easier, and it is far easier to set yourself a time goal rather than a fraction of a mile. If you ran for 30 mins 2-3 times a week, then that is a goal in itself. Then you can introduce a longer run of, say 35 mins, and leave the others at 30. Then move it up to 40 mins and so on. By doing a longer (time) run, mixed with the sorter ones you will find that you will improve rapidly, so that the 30 minute runs feel refreshing. A lot of people concentrate on time running rather than distance because once you are running outside, it is difficult to get the distances precise, and as you get fitter, your running route will take less and less time. What was originally a 30 min route, might become 25, or even 20 mins - over the course of a week, or month, that is a large amount of time that your not running!
Keep it up, the rewards are huge!