I have a main folder for each year. Within that folder I have subfolders named with the format yyyymmdd_Event name or location. Makes it pretty easy to find individual shoots. Then I use a bit of fine tuning on import by using presets that include keywords. I usually only add at this stage keywords for the place name and event i.e. airshow,railtour,event name or whatever might be appropriate.
One useful tip I have picked up is to use keyword hierarchies. For example i have a keyword hierarchy UK/England/EastMidlands/Leicestershire/Leicester. By just adding Leicester, LR adds all the others for me. By adding another keyword hierarchy of Transport/Railway/Trains/Railtours, I start to get more future searching flexibility. By following this approach with each import I can easily search for any railway photos taken in the east midlands even though I didnt specifically have to enter those keywords manually to each photo.
The more hierarchies the more flexibility. This approach has saved me hours over my previous methods - I now only have to enter 5 or 6 keywords and LR adds in the others. It takes a while to build your hierarchies and then revisit your old photos, and I still have to fine tune them occasionally but the plus side is that the system has dragged out some real gems I had long forgot about.