How do you route a spiral ?

I've tried freehand but the router bit always seems to pull to one side causing very wavy lines that don't look all that great.

Thanks for any advice!

Arms of steel...and a very sharp, preferably tungsten carbide, corebox bit.

you don't.

Personally... I created a guide/stencil for the bit. I've got a few different patterns.

I have never had any luck with doing these with a router. Use a 3/8 bent V tool and take it down slow. Don't try to remove to much all at once, start off small with your first pass maybe 1/8 to 1/4" and keep going over it. you can shave it down in no time and this way you wont have to worry about breaking off the peaks. also remember you don't have to use the entire V edge once you start getting deeper, one side of it will clean up any squiggles you may have had.

I only just thought this idea up but it should work, it is how I would try it.
Once you have the first part of the spiral started you can make a guide to attach to your router at exactly the right distance you want the lines apart.Put the guide into your start point and it should follow round and round in circles to create a perfect spiral.
Hope this makes sense