While we’re at it:
1. Don’t use a wet sponge. If you have a good soldering iron with good tips, you’ll want to use something that looks like a ball of metal shavings instead. It’ll work better, and you won’t oxidize your tips. They’re cheap and last quite a while. Some nicer irons ship with those in addition to or instead of sponges. I haven’t had much luck using these with cheap soldering irons, though, for whatever reason.
2. With a bad soldering iron, you’ll likely find yourself stuck in a cycle of cleaning the tip, tinning the tip, removing oxidation, and, ultimately, replacing the tip. It’s horribly frustrating. If this sounds like your soldering experience, ditch the wet sponge and get a better iron. It’s not you; it’s your tools.
3. Prep is important, especially when doing repairs. Older electronics have a lot of oxidation and are harder to solder. Spend more time on prep, less time on soldering. Don’t try to reuse the solder that’s already on the board.
4. Get Kapton tape (generic name: polyimide tape). Don’t bother getting a combo pack of different sizes; just stick to the half-inch size. Use it copiously. It’s cheap on AliExpress and will save you a lot of trouble. Tape All The Things. Avoid electrical tape; it melts, ruins soldering iron tips, and leaves a nasty residue.
5. Cheap dental explorers and scalers make for great prep tools. They’re cheaper than picks you might get from a hardware store, and they’re usually sharper.
6. Get desoldering wick and flux. The flux core inside the solder often isn’t enough for repair work. Soldering wick is the best way to remove old, stubborn solder. Soak it in flux first if you’re really having trouble. Some people say to get high-quality desoldering wick, but I’ve found soaking cheap wick in flux to be about as effective.
7. I keep isopropyl alcohol in a little squirt bottle and use it to clean off any grime, electrolyte, or whatever else might have accumulated on the PCB.