I had been running on the treadmill at the gym and I was at about 3 miles and my pace was just under 10 minutes per mile so I figured that I would train by time and not miles, since I didn't have the equipment to track my mileage.
On my calendar I wrote down how many minutes I was going to run for. My first week was 30 minutes, and then I would add 10 minutes every week. The week of Thanksgiving was 60 minutes and I kept it 60 minutes the week after due to the holiday and company in town. Last week I reached 80 minutes (about 8 miles!) I have 6 weeks left until my race (Saturday, January 29th)
Make sure the race fits your schedule! Don't just close your eyes and let your finger land on a race and pick that. For me, I will only run on Saturdays, because it's important for me to keep Sunday open for church and family.
Location and Time is important to consider. Some races have a very early start time and if you live pretty far from the race, you need to consider traveling time, checking in, and time to warm up. Races are supposed to be for fun, and don't do one that you know will just stress you out and not let you enjoy or do your personal best.
Clothing. I'm now learning about purchasing the right clothing for running, and I'll explain later why. But when I started, shorts are a must for me. My lower body has it's curves and the feeling of material rubbing together is quite irritating and will distract you the whole time during your run, so if it's the same case, shorts or better material is a good option.
Also hydration, Before, During and After.