The Megs kit comes with two clay bars. Open one, tear off half and that should be enough to do the entire car. Either warm it by putting it into some warm water or just keep kneading it (bit like with a stress ball) until it's softer. Flatten it out (i use a diameter of 5-6cm) and spray a part of the car. The best bit I find is the C-pillar near the roof. Spray with lube (2-3 sprays should cover the relevant bit) and just rub the clay on the paintwork. It should glide along. If there's a bit where it 'jams', you need more lube so spray. Once you've done a section, wipe off the lube with the cloth and move on to the next section. Break the car into sections mentally and work on one bit at a time. Check the bar after each section and if it's dirty, fold it over, flatten it again and carry on. If it's dirty everytime you fold it (ie no clean clay left) use the other half of the bar you saved. If you drop the clay on to the ground, chuck it away. Otherwise you'll be scraping stones into the car!!!
