[Pete]

I don't know whether this is obvious to most people, but it seems to work better for me.

When attempting to unlock your phone, don't look at the red light on the left, look at the camera on the right instead. It might also help to angle the phone so that the camera is pointing between your eyes.

I seem to get a better hit rate doing this

[A_Pieman]

Also when it says move closer moving the phone towards me normally recognises straight away.

[dKp1977]

I'm usually looking at the Microsoft logo and it's working perfectly fine for me. Will try and see if shifting my look a little more towards the right will improve it further.
Thanks, Pete. :)

[Edit]

Huh? Where's the "thanks" button gone? OO

[Pete]

I have a feeling that you're supposed to be following the advice of the animation to some extent as well, I think that it's trying to prompt you to open your eye wider when it can't see enough of your iris. It could also be just random animations.

[mathewhayward]

I've never had a problem with Windows Hello and I only trained it once and that was when I set up my phone initially. I just look at the 'Looking for you...' text when unlocking and it finds me every time