How can I go about developing my ability to taste flavors in coffee? I've been home-roasting coffee for over a year now, starting with stovetop pan roasting, then moving up to an air popper, and then a small roaster this Christmas. I'm at the point where I can tell a light-roasted, acidic Ethiopian from a dark Indonesian blend, but beyond that I'm frustrated by my inability to pick out specific flavors from one coffee to the next. 

Anyone have any tips/tricks for developing this? Or some qualities that vary across coffees that are easier to taste for along with vocabulary to describe what I'm tasting?
There are several approaches that can aid in developing your palate.

Cupping

The preferred method of tasting coffee. This requires only a cupping bowl and spoon. Dose out coffee, pour in the hot water evenly, and at 4 minutes skim off the top to remove the crust while carefully not disturbing what has settled at the bottom. Wait about 12-14 minutes for the coffee to cool to a desirable drinking temperature, and slurp the coffee with the spoon.

Types of flavors

There's a variety of descriptions you can use to describe the coffee. Try describe everything. The mouth feel: is it full bodied or light? The acidity: Is it citric or stone fruit? The Smell: What are the aromatics?

Note keeping

Every time you taste coffee, keep notes of what flavors you taste. Basic notes of chocolate or smoke are fine, more nuanced flavors like cherry or plum may come out. Don't be afraid to write exactly what comes to mind. If the coffee tastes like captain crunch then write it!

Comparing coffee

Don't just taste your coffee by itself. Compare it to other roasts you've done. Compare it to coffees from other cafes as well. Note the differences.