Bit of an Agony Aunt type question this, but....
When I get a new soldering iron tip, it only lasts for a very short amount of time before it gets covered in muck and won't melt solder. My current one for instance is a chisel-type- I've managed to keep a silver patch on the the two flat sides of the chisel, so solder melts OK on there, but on the rest of the tip, if you touch it to solder, it either just sits there, or the solder balls up and doesn't wet the iron.
I see videos of Dave and others touching the soldering iron to things and it actually getting hot! I'm so jealous.
I've got a sponge and one of those golden wire wool things. Using them does help keep the iron clean, but it still gets steadily worse. I'm using lead-free solder.
Basically, I don't want to keep buying tips since I'm obviously doing something wrong and destroying them.