Be prepared.
Before I take on any new mechanical job, I go straight to Google or YouTube and find how-tos for the job. I usually watch more than one. Last weekend, I did the rocker arms on my van, chasing the dreaded “Pentastar Tick”. Had I stopped at one video, I wouldn’t have found several tips and shortcuts that saved me hours of time. I take notes and write things down.
Organization is a form of preparedness. See, I’m not a naturally organized person. I am a “I think I saw it in this pile over here” person. But because I am so forgetful and scatterbrained, I desperately try to be organized when and where I can. That means having places for my tools. Gathering up the ones I need before I start my project, so I’m not spending half my time wondering where the 1/4 flex extension is. I use one of those compartment trays, like the ones for parts storage or tackle boxes, to sort bolts as I remove them, because I will forget. I keep an old long-handled ratchet with a 15mm socket on it hanging next to a strap wrench and all of my oil supplies, so I can do an oil change in 15 minutes.
I prepare myself to take at least twice as long to do a repair or maintenance than I think it’ll take. If I think a job will take half an hour, I give myself an hour. It sucks to run out of daylight or miss dinner because you’re still trying to find a nut that rolled away, but it happens - so be prepared for it.
Be prepared to spend more on parts or tools than you thought. If you’re on an extremely tight budget, consider waiting (if you can) to save up more money. If you plan ahead for a repair, you can often find parts cheaper online. Don’t cheap out on parts unless you have no choice - you don’t always have to buy the best, but do your research and stick to name brands. No-name Ebay crap is no-name Ebay crap for a reason. I went through three sets of struts on my old Neon back when I was “trying to save money”, when I could have just bought the Monroes or KYBs and been done with it.
And be prepared that sometimes, a job goes sideways, and you’ll either have to come back to it later, or take it to someone with more experience and patience than you have.
Making a plan of attack is incredibly important in wrenching. You can try to roll with the punches, make up a game plan as you go along, but that won’t work as well as getting everything laid out from the start.