For instance, I have a friend who just can't help himself constantly saying "ok". He'll say things like "ok, now we're going to [...]" or "now we've seen that, ok", and I'm just wondering what this practice is called.
I used to think this sort of thing was called a "verbal tic", but according to Wikipedia:
Phonic tics are involuntary sounds produced by moving air through the nose, mouth, or throat. They may be alternately referred to as verbal tics or vocal tics, but most diagnosticians prefer the term phonic tics to reflect the notion that the vocal cords are not involved in all tics that produce sound.