I totally agree Murf. As someone who unfortunately has to spend a bit of time on the M25 and M4 commuting into London most days, I get to witness atrocious driving almost every day.
In addition to your great tip "assume all drivers are out to kill you"
, I would add: keep space around you whenever possible, don't ride parallel to a vehicle in another lane (be just ahead or behind them so they don't take you out when they suddenly change lanes without indicating), keep your radar (brain) switched on all the time and be 100% alert of all other traffic around you. Don't retaliate with a cager who has just done something stupid - just let it be, breath and let them go on their merry way. Use plenty of life saver checks, and finally... don't rush decisions.
Ride safe out there all.