Years ago I worked for a tiny computer electronics company. By tiny I mean it was the owner, his girlfriend, my best friend Dave and me. When we weren't goofing off I did alot of soldering. From what I remember, this was the proper way to tin a soldering iron tip. You want to tin the tip so solder will stick to it. Then you can transfer the solder to your joint and hopefully it will flow nicely into the joint.
First off, while the tip is cold, you want to get it nice and clean. Use a stainless steel wire brush, or you can use fine sand paper.
Then wrap the tip with solder.
Now heat up the soldering iron. After a bit, the iron will get hot and the solder will melt. Then brush it off and wipe on a damp sponge. Here's an action shot of the solder melting.
And viola! Solder will now stick to the tip!
When solder stops sticking to the tip, just do it again.
I am no expert on soldering, so if anyone has any more helpful hints, please chime in.
Tom
First off, while the tip is cold, you want to get it nice and clean. Use a stainless steel wire brush, or you can use fine sand paper.

Then wrap the tip with solder.

Now heat up the soldering iron. After a bit, the iron will get hot and the solder will melt. Then brush it off and wipe on a damp sponge. Here's an action shot of the solder melting.

And viola! Solder will now stick to the tip!

When solder stops sticking to the tip, just do it again.
I am no expert on soldering, so if anyone has any more helpful hints, please chime in.
Tom