How to Get Faster using the Fridrich / CFOP Method

[Dacuba]

You could make a video, then people can tell you what needs the most practise, so you can get sub20 as fast as possible.
Wouldn't be surprised if your algs are terrible slow.

[Ninja Storm]

I'm a 3LLL and I'm sub-20...

It's all about practice. Know exactly where your first F2L pair is as soon as you finish the cross. Drill on each part of the solve, and learn to recognize F2L, OLL, and PLL cases within half a second.

Practice OH. This lets you look ahead more, and makes you more conscious of where the pieces on your cube are.

For the hardware part: Is your Dayan Guhong properly lubricated and tensioned? How often does it pop?

[Ranzha V. Emodrach]

Find out where your problems areas are. It's probably due to slow transitioning. Find where you pause and make yourself not pause.
This might help.

[AndersB]

Your F2L seems fine, but practise making more crosses on the bottom, and of course, don't forget to lookahead. Your LL, though seems quite slow to me. Make sure you know good algs (more in the wiki), and check Badmephisto's videos out, for some recognition tips. Also do OLL and PLL time attacks to practise your algs. If you haven't lubed and tensioned your cube correctly, also do that.

[Kirjava]

knowledge and speed have no direct correlation

[Ickathu]

What Kirjava said.

I learned full OLL and PLL and only averaged 30... So I practiced, and now still only average 23. My LL algs are really slow, and my F2L is pretty slow as well (12-14 on average).

Short answer: Practice
Long answer: Practice more.

[samchoochiu]

pll recognition should take 1 second after practice

[Sillas]

(Practice + Practice + Practice + Practice + Practice + Practice + Practice)³¹²³¹²
It take time and need training

[Sahid Velji]

I'm pretty sure a lot of people know the full method, including me, but are still not consistently averaging sub-20.

[Cubenovice]

knowledge and speed have no direct correlation

This!
I know full OLL and PLL and my CFOP average is still only 34 seconds
I can also solve in various other methods but always slow...

Note that I still think that I'm not very knowledgable.
Knowing full OLL PLL is still just one part of CFOP.