I organize my gallery by series and then by 
episode # (OP/Eyecatch coming before all else).  
I try and screencap as many of my cels as I can, 
so as long as I'm figuring out what ep they're in 
I might as well organize 'em that way. ^^  In 
theory it also prevents spoilers since anyone who 
hasn't watched all of a series can stop looking 
through the cels once they get to cels in eps 
they haven't seen.  If I have several cels for 
one ep I try and list them in order, but I'm not 
picky about it.  If I can't nail down an episode 
ID the cel is placed at the end of the gallery 
for that series.

If I have less than 3 cels for a series they get 
lumped in the Misc section, which is currently 
organized alphabetically by series title.

-Pasiphae