All good advice here. Depends on how 'perfect' you want to go. Even without a DA, if you were to clay bar before polishing you would see and feel great results. My $0.02 would be to wash with an aggressive cleaner (like stardrops) to remove the previous waxes and oils, then clay bar. Claying takes away the rough 'grittiness' you feel when you run your hands across the paint. It removes surface contaminants and fallout. This can be best experienced when you feel your car's paintwork through a thin plastic carrier bag (like a Tesco's shopping bag). Do it before you clay and then use it to gauge the results after. When I first clay-barred my car it was a revelation to me. So easy, but so effective.
When that's done, rinse down, and apply a good polish. A polish is a compound that will refine the surface. In it's purest definition, it will purely remove material and smooth down your paint. But will leave it open to the environment and will quickly deteriorate back to it's previous state. After clay barring, you will find that you may not have to do much polishing. The surface will be much smoother than when you started.
The next step is to protect what you have just done, which is usually done with a wax, glaze or sealant (often referred to as an LSP (Last Step Process). Also, some people here have referred to 'fillers' and that's just what the are. They fill and hide scratches. Some products like AG SRP have fillers. Not disrespecting SRP at all. It's a fantastic product. It is what you could describe as an All-In-One (AIO) as it cleans, polishes and contains a sealant.
If you want to skip a step, you could just clay bar and then apply a few coats of SRP. You won't be disappointed.
