Yeah, I'm going to do this as a series of posts. If I tried making it one long post it would be wa-a-a-a-a-aaaaay too long and put to sleep anyone who tried to read it. Much of it will be pretty “basic”, stuff I wish I'd been told (or had had sufficient sense to ask) when I was just starting.
Everyone starts somewhere; where we go is mostly our choice. My first race in 2011 was a 5K, with a finish time of 49:30. It's not fast, but it was what I could do at that time. My goals that morning were to finish, with a time under an hour, so I was very happy. Fast-forwarding some 4 years, I did my second 5K (weird, I know). My finish time was 42:31, nearly 7 minutes faster. Though I took rather circuitous and indirect route, I did the work to improve.
Whether you're a speedster or a reforming couch potato, you are where you start. That, not some other person's abilities, is basis for gauging progress. If you're the reforming couch potato, don't be ashamed of it. You're already making progress, because you've started. If you're the speedster, don't be particularly proud of that. You may become a world-class runner, but that isn't you, yet.
Growth can be in multiple directions. You can go faster. You can go longer. You can take on more difficult terrain. The big thing is to start, and you don't have to choose just one growth direction. For me, 2014 and 2015 were years of going longer (specifically, more races than the previous year) and on more difficult terrain. On the other hand, my speed did suffer some in “flat” half marathons (though an injury contributed some to that).
In whatever endeavor, deciding to start is the biggest decision. Choosing to grow, to improve, is the second-biggest decision.