Pounds, ounces, grams and kilos ... it really is all academic to me. Despite being part of the new metric generation an ounce of butter is still somehow easier to judge than 25g, conversely visualising a Ribena carton provides the most useful reference for judging liquid in units of 250ml. To be honest I'm appalling at estimating, so most of my cooking relies on handfuls, spoonfuls and ratios. This relaxed attitude to quantities is all very well in my own kitchen, but I am aware that the resulting muddle of grams and pints, of teaspoons and millilitres is probably a little confusing.
So, the things you need to know - teaspoons and tablespoons - I measure these with the metal spoons from the cutlery drawer, and use them slightly heaped. My pinches of salt are big, as are my handfuls of herbs. Temperatures - my oven has a fan, so the temperatures listed work for that I'm afraid - 150 is low, 190 medium and 220 high - I have no idea of the gas mark or Fahrenheit conversions (I can hardly even spell it for a start).
I will endeavour to stick to one system or the other within the limits of a particular recipe, but I can't seriously contemplate going fully modern. I don't think pastry was ever made without the reassurance of ounces.