as above mate.

First give the car a good rinse over to get ride of any loose dirt
Then get a washing mit and give it a shampoo
Then re-rinse and towel dry
At this stage I try and remove excess tar spots with a tar remover fluid - you could do this during clay baring but prefer to get it gone and not run the risk of dragging it around on the bar.

Then get a meguires claybar kit (approx £15.00 for the kit includes bar and lubricant).

It is pretty easy, give the bar a flatten out until it is soft and patty shaped and them spray the lubricant onto the panel. Then use the bar in the same way if you were lightly sanding.

You will feel some friction but after a few passes it will glide and you can move onto the next area.

Go gentle, keep lubricated and you will be fine, make sure you dont drop the bar on a dirty floor etc naturally.

The clay bar works by allowing grit to sink into the clay away from the panel unlike normal polishing which leaves you dragging thr grit round in circles as you polish.

Once you have done the whole car wash it again and towel dry.

NOW, you will notice polishing and waxing the car is FAR easier as the paint is griome free and buffs off easily.

Give yourself a good 4 - 5 hours to do it properly, but the results will be worth it, PLUS it will mean future cleans are far easier.