Once you've gotten your body down to bare steel, you'll be able to see all of its flaws. Even nice examples of 20-year-old cars will have some dents, dings, and possibly rust. Some of the minor imperfections will be harder to spot, requiring an educated feel to locate, usually by rubbing the open hand back and forth along a panel. Fixing dents and rust does require varying degrees of skill, depending on how much work is required, but it is possible for the novice to tackle some of this, even if the pros have to be recruited to finish up. The key is not creating more work in the process.
Obviously the simplest way to deal with damaged body panels is to replace them. For older classics, this may mean scrounging the swap meets or the Internet, though the list of reproduction sheetmetal for muscle-era cars is growing steadily. It comes down to determining whether to replace or repair, which should probably be based on how much work is required to repair, and how that compares with the cost of replacement. Remember also that while fenders and doors are relatively easy bolt-on items, quarter-panels and rocker panels are not, and must be cut and welded (see "Reconstructive Surgery," page 32), which basically requires professional installation and significantly increases the cost of replacement.
Cars built during the '60s and '70s were notorious for rotting, even when based in mild climates. Much of the problem was due to poor drainage and leaky body and glass seals, so rust can even plague cars that have never seen snow. Short of replacing rusted panels, proper rust repair mandates welding, though a 110-volt MIG-welder is usually sufficient for sheetmetal work. Some small rot holes can be patched with pieces of sheetmetal stock, while larger holes may be easier dealt with using specifically stamped patch panels. Patching with sheet stock is pretty straightforward: Trim out the rusted section, cut a piece of new steel to match it, patch it in with small welds, spacing them out to minimize the concentration of heat, and continue around the panel until there are no gaps between the patch and the panel. Then grind down the welds and smooth the repair with filler. The better you are at this, the less filler you'll need. Stamped patch panels will require more specific trimming of the rusted section and careful alignment. If you have little or no experience but do have access to welding equipment, practice on junk panels first. If you think it's completely over your head, talk with a professional for an estimate.
This is the area of bodywork that probably requires the most skill and experience. Working sheetmetal into shape could be considered an art form, particularly when true craftsmen work their magic. Shaping body filler for the final finish presents yet another challenge. Many novices have driven themselves nuts attempting to tackle panel-straightening alone, so don't feel bad if you have to bring in a pro to get it right. Entire books have been written on metalworking and other forms of body sculpting, so we can't even begin to go into the process here. However, if you think you might want to attempt this, get some junk panels and some good reference materials, and give it a try. Even the most skilled pros will tell you that practice has more to do with successful work than anything else.
If you have no intention of becoming a panel-beater, you can probably shave some shop time off of dent repairs by prepping the area yourself. This will consist of basically grinding out all paint and filler in the affected area and perhaps removing other parts and pieces that may provide access to the back of the dent or hole. Don't remove the panel without talking to the shop that will perform the repair, as many pros prefer to work the steel while it's still mounted, since the panel is better supported that way.
There will be plenty of sanding involved in any body project, and block-sanding is usually the final process prior to paint. If you don't know what you're doing or what you're trying to achieve during this step, you can waste a lot of time and effort. Block-sanding is the process of hand-sanding with the sandpaper attached to a sanding block or a long board. The idea is to sand the panels until they're perfectly smooth, though they should be almost there before this stage even begins. The goal is to eliminate the small waves and surface imperfections so that after the paint is applied, it will be mirror-straight.
If you want to attempt to do the block-sanding to eliminate some of the grunt work from your shop bill, talk to the technicians who handled the previous work, especially if they will be the ones to lay down the paint. In some cases, they may not want you to be involved in this process, as it is possible to screw up the surface even further, rather than smoothing it. If they are willing to work with you, listen to their advice and remember to be gentle--any harsh sanding here can create ripples in the final finish.