Sure. You'll find them out by messing around. It's hard to document that kinda stuff.
It'll surprise you how much you can use cancellations. Like between every single alg.
Do you rotate? If so, stop doing so and you'll notice that your lookahead starts to go crazyfast. I never pause in my F3L
Do you have corners already solved? If not you don't get the advantage of being able to use all the mad tricks that work on 5x5x5 too.
Oh. I've been doing my F3L very systematically, so I haven't really been messing around much. I suppose I should.

I rotate a lot. I didn't realise that was bad. Thanks, though.
I assume you mean the corners of the first layer. Yes. I always have them solved by the time I get to F3L. Also, I only have a 5x5 (no 4x4; it broke) at the moment.
Lastly: What are cancellations? And how can I incorporate them into my solves? (Sorry if that's a stupid question; I genuinely don't know, though)
PS: I still haven't timed myself with K4, so I have no idea where I'm at.
Did you read the ELL page on my site?

Also Dan's video.
Um. Don't think so. Do you mean
this one? Also, Dan's video? I don't know who that is, nor do I know the video (most likely).
PS: I currently don't have a lot of time on my hands (so can't do that now) and shall probably get back to this later, but I'm replying so long so that I don't lose the reply due to the speed at which this thread moves. >.>
Thanks for the reply. Much appreciated.