Lube, lube, lube and a bit more lube. Keep it soaking wet all the time. You can get dedicted clay lube in a spray bottle but all I use is a strong mix of car shampoo and water, seems to work fine. Either flat it out like a bar of soap and rub it over the paint work with your fingers or roll it into a ball and hold it in your hand, whichever works best for you.

Oh and if you drop it on the ground, throw it away and start again. as it will pick up all sorts of shit. Get some tardis and some Iron x and use that on the paint work before you clay as it will dissolve most of the contaminates in the paint before you start to make the laying process easier.

You can also put your hand in a thin sandwich bag or similar then rub it over the panel to feel all the crap stuck to the paint. You've finished claying when it is smooth as glass!