The best way is to prevent the soldering iron tip from oxidizing! This means that after every soldering operation you clean your soldering tip (dry / wet) and then tin it before you put the soldering iron back in the tool holder. If it happens that the soldering iron tip is oxidized, you can clean it with a “tip activator” and / or sanding block / brass brush. All this is discussed in the practice part of the IPC-7711/7721 training.