Was this in the US? It’s not triggering my US herpetometer (I’d think whiptail, but I’d expect a little more of a pattern on the back in the US), though granted I am out of practice 
. But it looks a bit like some sort of Teiid (if it’s New World).
Skinks usually (but not always) have proportionally smaller legs and a more “neckless” appearance. Also they often (but not always) look a little “shiny” or smoothly armored with glossy, circular scales. This is a good photo for a very general example of the average differences between the two. But they can absolutely be confusing - i.e. skink vs whiptail.
Ruby-crowned or Golden-crowned? I’ve never gotten a “good” shot of a Golden-crowned either 
. They always seem to be bouncing around high oak trees in the shade on the rare occasions I run across them.
I’ve had better luck with Ruby-crowned Kinglets, which can be pretty common migrants in season around here. I find chasing them in trees and high, dense brush to be a little frustrating as well - as you said, small, fast and frenetic. Doesn’t stop me from chasing them (because compulsion), but I don’t often fare well.
The key with those for me is to A.) find them near eye-level or lower and B.) anticipate and get in front of them as they’re feeding towards you, which of course can be easier said than done. Around here I find in open scrubby areas they like gleaning aphids off stuff like wild anise or other stubby bushes. The nice thing about certain tiny birds like kinglets is that you are so much larger than any predator of them that they can be pretty bold and oblivious of you if you stay still. If you can get into that situation, they are actually one my all time favorite little birds to shoot.
Just don’t mistake them for the dreaded Hutton’s Vireo, that loves to confuse birders!
