Hi Julian,
Wow... so excited.. never got someone to actually ask a follow up question.. Does this mean I might know something? (but then the more you know the more you realize you don't know, right?)
Anyway,
The short answer is that I created static collections one at a time (ie. Christmas 1980, 81, 82, etc., or "my cats") then worked on that group at one time. I do not find creating keywords first helpful, as my "best laid plans" for keywords seems to leave me with a lot of "empty" keywords.
More answer:
My personal experience: When I first started keywording my already large family photo collection in LR, I wasn't sure how to shortcut this rather time-consuming process. I decided that by "chunking" the job down, it would seem less "overwhelming". My photos were imported into folders by date and often with a 1-3 word subject, like "Christmas" "Backyard birds", etc. So, starting from the oldest pics, I selected certain folders that I knew, based on date/topic were going to have a lot of the same keywords, and placed them in a static collection, ie. photos from December 24-25 from various years went into a static collection. From there I went ahead and began keywording that collection - my favorite technique was to "spray paint" photos with 1 or 2 keywords at a time. You could accomplish this by simply selecting those folders and keywording on those selections, but since I get distracted often by various projects, by creating static collections, I was able to work on a group of photos, leave it, then come back and work on them again later. Eventually, when all the photos are keyworded as I desire, I just delete the collection, or alternatively, I have created smart collections that "grab" any photos with say "Christmas" or "Jasmine + cat" and create the collection for me. That way, with my newer photos, which I try to keyword right away, once they are keyworded they automatically get added to the appropriate smart collections if they meet that collection's criteria.
As for creating keywords before vs. during the process, I'd much rather just create the keywords on the fly, and when needed I create keyword collections to help me remember which keywords to use on a particular topic (ie. a "Christmas" keyword collection might include "Christmas", "gifts", as well as the names of the people most likely to be in those pics (mom, dad, husband, aunt, uncle). I find the keyword collections helpful but limited by their numbers- I'd like to see say 18 vs. the current 9 keywords per colleciton limit.