Thank you everybody for all of your help. My favourite ruler is my creative grids 12.5 inch - no slipping, and lovely clear markings. I may have to invest in their 12.5 x 24 one day. I'm not quite at the level of more complex patterns yet, but the only speciality ruler I have got my eye on is one for 'Storm at Sea'. I cut sitting down at a large desk with an A1 board. I've just got my sewing room set up so that I can have my table and machine in front of me, and my iron just to one side - so handy
I've also learnt why it's so annoying if the shop hasn't cut your fat quarter straight - more wasted edges!