You've received some great info here. I would add the following, and I hope this doesn't make things sound worse or overwhelming. These are all just best practices and learn from my mistakes kinds of pointers.
1. Agree with starting with an All-in-One. The Griot's Ceramic All-In-One is excellent. Just remember it's an all-in-one... that means it is a compromise both in terms of correcting ability and all out protection durability. You will not get as much correction as a dedicated polish and you won't get as much protection as a dedicated sealant or coating. That's okay-- this will still make your paint look much better.
2. Don't skimp on the decontamination step(s) if they're needed, and I suspect they will be in this case. Wash thoroughly (pay special attention to things you might not normally such as cracks and crevices. You want to flush the paint and seams of as much dirt and grime as possible so it doesn't come back to haunt you when you're polishing. A soft brush helps a lot here.
2. Since you're new to machine polishing, I'll tell you something that took me longer than it should have to understand. That is, don't try to do too much polishing with too few pads. In other words, buy several pads (even though they're expensive) and change them out after every few panels. As you polish, the pads will pick up dead paint (and other things) and that embedded contamination will reduce the cutting ability of your pad (or worse, scour your paint as you polish). This is called residue control. Alternatively, you can buy a special pad cleaning brush, or better yet use compressed air to blow your pad out frequently if you'd rather not buy several pads.
3. Use LED lights to examine your work as you go. While this may seem tedious, it's better to do this and uncover mistakes/trouble spots as you go rather than have to come back and hit them again IMO.
4. Make sure your back plate continues to spin as you polish. If it does not, you are not getting much work done and are probably putting too much pressure on the machine. A mark with a Sharpie on the backing plate can be an easy visual cue that your pad is still spinning (not just jiggling).
5. Never turn the machine on without the pad flat on the surface, and never lift the machine off the surface while the pad is still spinning. These will lead to you slinging product all over and making a mess.