Door panels ?

Working with old, brittle plastic is always risky. Expect some damage to tab type fasteners, no matter how careful you are. If you don't break any, consider that the exception, and not the rule. There are specialty tools that minimize damage, but they are often prohibitively expensive or unavailable for the DIY'er. A couple common and simple tools that are really helpful are wedges and long-reach tools. Handy wedges, such as plastic felling wedges (used for felling trees) can be found at hardware and home improvement stores (and anywhere that sells/services chain saws). Long reach tools can be anything from screwdrivers to weed-popping tools. I like the weed poppers (long screwdriver like tool, with a wide, flat, forked end, robust handle, usually with a couple slight-angle bends, and about 20-40 cm long, modify as necessary). You can also fabricate a good long reach tool by simply flattening the end of a length of metal rod. Good lighting is also important, so have a good flashlight handy. Check everywhere for screws, especially embedded into carpet panels (screw heads will often be below the pile surface).

Anyway, most GM vehicles aren't too complicated, but there is usually a lot of plastic fasteners, retainers, and aligners involved. Breaking some of them may be unavoidable, but most often can be restored with a little ingenuity. The metal clips over plastic tabs almost always weaken their grip once removed, so rebend them a little so they grab a little more once reinstalled to prevent rattles and maintain alignment. Most panels are secured at the bottom edge with screws and/or friction fasteners/tabs, and metal edge clips at the top (once the bottom and middle fasteners are free, the top lifts up and away). Youtube is also helpful for getting a look inside a panel before you dive into yours. Most folks make note of hidden fasteners. Let them show you how they broke theirs before you break yours. Even good drawings are not of much help. If you have power windows/locks, simple connectors are almost always accessible, and some are removed with handles and levers before removing the panel.

If you are repairing a window motor, it's always a good idea to replace the register and lubricate tracks, as well. Slow power windows are very often a combination of tired motors and worn registers. Plastic guides work much easier with a little silicone grease to slide on. It's also a good time to replace old radio speakers, sticky switches and weather strips/wipers. The key to solid door panels is removing them as little often as possible, and restoring fasteners as much as you can. Every time they are removed, they go back on little looser than the last time.