Soldering iron tip grinding
DON'T grind your soldering tips. It will ruin them. Good quality tips are made from copper with a thin layer of iron or another metal on top. The copper conducts the heat, and the other metal prevents the copper from corroding. You can buy new tips of any size and shape you want. They are pretty cheap. There is usually a tiny screw on the side of the soldering iron near the hot end that lets you change the tip.

Here's a cross-section of what's inside good tips (image by Hakko)