Tips for Improving Battery Life? (15" rMBP)

I currently own a 15" Retina Macbook Pro that I got in late July. While the battery life isn't really "bad," there are many times where it gets low enough to make me a little nervous. This usually occurs when I'm sitting in a class and am too far away from a plug to keep going.

I never leave it plugged in when it's fully charged, it will get down into single digits on a frequent basis, and it spends most of the day between about 40%-90%. I'd say I get an average of about 3-4 hours of life running nothing but Mail and Evernote at full brightness. Is this normal? Low? High?

Mainly, I'm just curious if you guys have any tips or rules of things I could turn off, turn down, or something else that you know of on a Macbook Pro that would get me some more longevity out of the battery.

Thanks! :)