Getting started with dumbells ...

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Since the end of May, I've lost around 34lbs using MFP. I'm now within about 6lbs of my goal weight, which is the upper end of the normal BMI for my height.

So ... phase two is that i'd like to tone my upper body a bit. I have a set of dumbells which have been in the box since I bought them about 5 years ago.

How do I get started? What exercises, how often, and what sort of weight should I be lifting to start with?