Secret is simple: Many have said here:
Do stuff you enjoy - it shows.
I have a pretty simple rule of thumb. After I'm done editing, I view the video AGAIN to make sure there are no crazy glitches, or sound problems, or I said something stupid along the way.
If during this viewing I nod off, go browsing, or shut it off, I do not upload it. If I don't want to see it, why should anyone else?
(I make some exceptions. sometimes I make a vlog I know is good, so I just encode and upload directly.)
Every now and then I go see some of my own fav videos. (the mt09 review, black suit zombie, the 5k sub tribute....) If I keep enjoying them, I've done something right!
Also, many, MANY of the subs are simply because of my bike reviews. At the start of last year's summer, I noticed there were NO reviews of the Honda CB500s. So I decided to make a review of all three, considering my most viewed vid at the time was my review of the nc700x. I sensed an opportunity, a gap in the "marked", so I went for it.
It payed of thrice:
1) Many MANY views and subs from that
2) I REALLY enjoyed doing those videos. really REALLY enjoyed them. (and it shows in the vids that enjoyment - which makes them entertaining)
3) Some dealerships are now calling ME when they get an interesting new bike to testdrive

(ok, well its ONE dealership. one. But I can embelish a bit, can't I?)
Due to the fact that many subs stayed for the bike reviews, my vids are usuall at the 1.3-1.5k views mark.