I've been working on cars since the early 1970's. My own and those of my family and friends. Repairs have run the spectrum from oil changes to head gaskets to pulling engines to replace internal components. In 40 odd years I've learned some things: *Keep organized. Make notes, take pictures, store bolts neatly. I try to thread bolts back into the holes they came out of as soon as the component is removed. That way, I don't have to sort a box of random bolts when reassembling. * Make sure all bolts are removed. Most items separate easily when all fasteners are out. The exception would be something like cylinder heads that can become "glued" in place. I've seen things ruined from pounding and prying only to find out that one bolt was overlooked. * Penetrating oil and heat are your friends when removing corroded fasteners. A heat gun works but so does a propane or Map gas torch. Be careful though. A torch can and does burn grease, rubber, and plastic. * Utilize your resources. A Haynes manual or FSM is invaluable. Internet searches can be a great help too. An older guy at a parts place can be a great source of information. * If you're frustrated or tired - STOP. Take a break, get lunch or quit for the day. Rest and a fresh perspective can do wonders for problem solving. * An engine needs fuel, air, compression, and correctly timed spark to run. Take any of those away and it doesn't. * Spend some time just looking at or listening to things. Cracked rubber (vacuum leaks), corroded connectors (electrical issues). Get a mechanic's stethascope (HF) - it will help you isolate noises, ticks, etc. * A good worklight is one of your best tools. So is a telescoping magnet pick up. * A small amount of copper antiseize on bolts subject to corrosion can make life easier for you next time things have to come apart. * Make a "don't forget" list for reassembly and hang it up where you can see it. Things like oil or ATF filled before startup. I once saw a guy ruin a freshly rebuilt engine because no one had filled it with oil. I'm sure there's a lot more. Experience is the best teacher. Anything else you'd care to add?