Anyone have any good tips for scanning negs to get the most out of them? Also, for colour/white balancing them?

The biggest thing I've learned so far is it's terribly hard to fix a negative/slide in post. Adjusting the scanners backlight levels is the most I do, and usually you can tell really quick if it's worth scanning or won't look good no matter what tweaks are applied.

A friend of mine uses the trays from Better Scanning and raves about them.

I think the best tip is the get the exposure right and you'll have to do very little post in the scanning.

Use curves to color correct. I shoot transparencies exclusively, so I always have to nail the exposure (which really isn't hard I dont understand why people think it is). Make sure your scanner and display are color calibrated. Other than that, make sure everything is nice and clean.

What kind of scanner are you using?

Also, a little protip for reversal film users: If you want to get a stop to a stop and a half extra of dynamic range dont blow out the highlights, then when your get your film processed push it a half stop to a full stop. Pushing the film will not increase highlights, but will develop the shadows.

I'm using an Epson 2450, but when I get ready to go to print I usually use an Imacon (likely will try drum scanning as well at some point).

Agree with the tips above. Consider wet mounting (look 'er up on google to learn about it - I know it sounds dirty, but it's not, trust me - just don't click on the wrong google results)

Additionally, I highly recommend not using film holders and either placing directly on the glass, or by using the Betterscanning plates. Betterscanning plates are nice because they use anti-newtonian coating, which means you won't get those drasted Newton rings that all the kids are talking about these days (or at least the cool kids who shoot large format).

And whatever you do: never.... never ever... use the auto calibration settings for your scanner...