Forward to back, but each cabin crew member will be assigned a few rows, so it's really 3 or so crew starting at the same time, from 6-12/14, then 12/14-19/20, then 20/21-26 all at once, rather than going from 6-26 one at a time. On 2 class then only 2 of course, 6-11/12-23.

If you're lucky the supervisior or even the purser (shock!) may help out and it goes faster.

On 2 class upper deck, you want rows 12+ if you want to see the engines.