I think what times you get are just a combination of everything.
Current mood: Happy sad, focused, distracted, thoughtful, worried, stressed, calm etc.
Cube: A good cube will help you solve faster, herp derp.
The cube you are used too: If I am used to a LingYin, and then I try and use a Mini Diansheng, chances are I won't be as good considering MiniD locks up more, is smaller, sometimes backwards color scheme. Most common example of this from my point of view is Rubik's Store-bought (most people's first cube) to a DIY of some sort. Huge difference. Once you are used to a cube you can use it to its full potential.
Cubing Style: If you are a heavy turner and you are trying to use a cube that doesn't respond well too it, you will obviously have problems. I think cubing style can be changed a little, but not a whole lot. It takes time, constant effort, etc.
Algs: If you are a right handed solver and you are trying to use LU heavy algs, it just wont work out to well for you. Kind of obvious.
Practice: If you take what you know, and keep doing it, over and over and over and over and over again, can be good and bad. If you have a bad habit and you keep doing it, it will just become cemented in your head and that isn't good. But if you have learned all you plan to know for the time being then practice is good and will help improve lookahead.
However, things like look ahead require that you actually try to improve, if you continue to just look at the pieces you are working with you will never improve look ahead, if that makes sense.
Method: Kind of related to cubing style, but if you are terrible at M and M' moves, and you try to use Roux, it probably won't work unless you really focus and try to improve your M moves.
Mental state: similar, yet different, to the "current mood" one above. If you think you can't get better, and just solve in a futile attempt to get faster (which you assume will never work) then you probably won't get much faster. But if you think you can do it, and try to, then you can. Cheesy? Yes, but it's true (at least in my opinion)
These and more affect your cubing speed in my opinion. Of course some are more important than others, and some play a larger role than other, but I think all work together to come out with you final speed.
~Chris
