What is the best-practice for circular lego staircase construction?
There's a brick-built spiral staircase in the Pet Shop:



That's definitely the most common way to do it. You just build up around a central point. This can be expanded to use longer or wider steps:




http://www.mocpages.com/moc.php/267772

You can also use 2x2 turntables if you need more strength and/or larger stairs:


http://www.popscreen.com/v/6UIWz/Tutorial-Lego-Spiral-Staircase