I used to help mask-out cars when I was a kid.
Knock off the wheel weights else there will be a spot underneath when you buy new tires and rebalance. You can also mask the the weights but that is up to the owner.
If the existing paint is good, light sanding with 220 grit on surfaces to be painted.
If there is rust, the rust has to be removed. Sand blast the rust.
Professional auto body paint stripper is caustic and getting nooks and crannies clean is difficult. A hood, door or fender yes but not rims.
Using auto body masking tape on rubber tires is a real pain. The rubber has to be really clean to make the tape (has to be fresh tape) to stick well. It simply peels off otherwise. We used a clean rag with lacquer thinner and wiped up to and sometimes underneath the edge of the rim. Rotate the rag to a clean spot then wipe some more. When clean, let it dry completely. Air hose the edge of the rim. Wipe again if needed. Tape (series of tape segments), then lap the tape slightly below with another row. On top we taped masking paper to completely cover the tire to catch overspray. One pass of the spray gun, no paint, will tell if the masking tape will hold. Back then if you sprayed enamel paint we waited till the next morning to remove the masking. Masking tape in the hot sun will turn to goo.
Remove the masking in the reverse order of installation. The last bit is done slowly. If the paint has bridged well to the tape (no gap or crack) you may have to help with a thin razor blade to separate. Slowly pull down and away from the rim edge, not up or out.
