Take a good long sniff and decide what you smell. Toasty chocolate, rosted, caramel, malty sweetness. The next step after evaluating the aroma is to check for clarity. Hold the glass up to the light. Check to see how well you can make out your fingers on the other side of the glass.
Clarity is a result of how well-fined or filtered is the beer.
Finings are used to attract certain components of a beer's make up. A fining will attract either yeast or protein and precipitate them out. A filter is either a sheet with certain micron holes in it, or a filter bed make of diatomaceous earth, either of which the beer is pushed through. Different styles of beers are meant to have different levels of clarity. A German-style Hefeweissen, for example, tends to be very cloudy because of the lack of filtration.