A lot of people would say that the first thing you should consider is shoes, gear, clothes or any other thing. But what I think is very important to keep you running for a long time is a GOAL.
The goal keeps you running even if it’s very hard to do. The first goal shouldn’t be very huge. Maybe it is to run 5k or to run 5k in 30 minutes. You can make any goal you want: to lose 5 pounds, to attend 10k competition this summer or even a marathon. After all, you goals should change – if you achieve something, think about bigger goal.
My first goal was to run 10k. Believe me, you can do it very fast, even if now 2k looks such a big deal to you. After sometime you will say “10k? Pfff, no big deal” 
So after that I thought about running a marathon. I did it twice. Now, of course I want to attend more marathons and my dream is to run 100k. So maybe next year I will be able to do that 
Goals keep you moving, not sitting on a coach. Don’t give up, you can really do it! But remember – you always get, what you are working for. If you think that you can just run once a week and your 5k time will be awesome – it won’t happen. You must commit. You must work. And believe me, you are going to succeed!
No matter how old are you – you can do it. No matter how is your physical condition now – you can do it. No matter if you can run just 500m now – you can do it!
Just you can say to yourself that you can’t. JUST YOU. So don’t give up on yourself 
Good luck to you