for me, it was a physical change. it took a while for my body to physically catch up to what i wanted to do. i'm a 'late bloomer' which is ok. i'm running well now.
seek a coach. find something that motivates you.
also, don't neglect the speed. if all you do is run slow, you will become a slow runner. feel free to add some strides at the end of your runs every now and again (a few times a week, barefoot if possible). distances can be anywhere from 50m-100m, and 4-10 repeats. also, if you feel like pushing the pace during a distance run--do it!
also, when setting goals, here is a good method to follow. make your goals SMART:
Specific
Measurable
Achievable
Relevant
Time-bound
example: I want to break 17 for 5k at the Spring Break Relays this upcoming track season.
specific? kinda. measurable? sorta. achievable? probably. Relevant? yes. time-bound? yes.
but lets work at this goal some more.
I will run 16:30 for 5k at the Spring Break Classic, by averaging 5:15 per mile.
Specific? yes, with a plan.
Measurable? yes.
Achievable? (like i said, probably. i don't know you, but i assume it's do-able.)
Relevant? yes, it's not a half-marathon or marathon goal!
Time-Bound? yes. the "spring break classic" is a generic track meet that i'm using here. it could be a conference meet, another invitational, or a road race (carlsbad 5k perhaps?)
go for it! keep us updated on this thread.