If you have a vinyl top then remove the molding separating the vinyl and paint. Drip rail chrome really should be removed also, but can be extremely hard to take off undamaged. If you plan on buying all new drip molding then definitely remove the old for painting. But if you want to keep the originals then it might be better to leave them on and let the painter mask around. If you have hub caps it's easy to just take them off. While the paint shop should completely mask all four tires, overspray can still find its way in. It's sometimes better to play it safe and just remove wheel covers.
Scuff for paint. Once your Mustang is totally stripped of exterior chrome it's time to scuff up the existing paint. The paint shop should do this also, but on the lower end paint packages they won't spend much time here. It's better for you to do it so you know it's done thoroughly.
Also, when checking the paint, be realistic and don't ignore areas just for the sake of convenience. It will cost you more in time and money later. Typically if one area of the paint is cracked or peeling, then the paint on the entire car is suspect. Maybe the rest of the car just hasn't quite reached that point of decay, but it will shortly. So if you only fix areas that look bad, you'll likely find that you wasted a paint job when the other areas start to crack or peel in a year or two.
Cold water paints of the casein type may be applied either directly to a plastered surface, or the surface may be first given a coat of primer-sealer to equalize uneven suction effects. The same is true of resin-emulsion paints, with the recommendations of the manufacturer of the product being given preference in case of doubt. Since resin-emulsion paints usually contain some oil in the binder, they should ordinarily be applied only to plaster which has dried thoroughly.
Airless Tip: If you have somebody who can start masking off the trim, have them start on that while you convert the airless to a new color. When changing colors with an airless paint sprayer it is a good idea to have a second bucket filled half way with clean water. Place the intake hose in the clean water gently without getting the old color everywhere in the water. Take the tip out of the airless and spray all of the old paint out of the hose and back into its original paint bucket. Be careful when doing this that you recognize when the paint starts turning watery. When it does point the gun into the first bucket and spray until it looks pretty clean. It doesn't need to be perfectly clean. When it looks good, clean off the intake line in the clean bucket and get the old color off the intake line. Now place the intake line inside of your new trim paint.
A large whitewash brush is best for applying the wash. One should not attempt to brush out the coating, as in applying oil paint, but simply spread the whitewash on as evenly and quickly as possible.
Another idea keeping Paint Brush moist until the next paint coat is applied (but not leaving for extended periods) is leaving Brush in container, wrapping top with plastic, sticking handle out the top, and taping around the can. This resembles the Maxwell House Coffee Container mentioned earlier. If plastic and masking tape is still not available, and time between coats is not very long, take that sopping wet rag, draping over the top of paint bucket with Paint Brush still in it. This technique works best when using Latex waterborne paints.