Hey Lloyd.
First off, give your car a good wash, then you want to use an iron fallout remover followed by a tar remover (if you need it).
Once thats done, either use a dedicated clay lube or plenty of shampoo solution, and clay the whole car, including the glass
Then just give it a rinse off, and dry the car completely.
After that, polish the car by hand or by DA. If you are using a polishing compound, I suggest using something like CarPro Eraser, to remove and polishing residue and oils. This leaves a perfectly clean paint surface, ready for a wax or sealant.
Then decide on your LSP, and apply a couple of layers (especially wax).
Hope this helps
Bertie