Choosing the Right Photography Umbrella for Your Needs
Your first and arguably most important task is to assess the particular needs of the shoot.
Is an umbrella really what's appropriate? Photography umbrellas provide diffused light for a scene. If you're trying to light a particular object from a particular direction, using a softbox might be more appropriate. On the other hand, softboxes take a longer time to set up, so if you need something quick, then some sort of umbrella might be a better idea.
There are also many types of photography umbrellas to consider using. The main distinction is between “bounce" or “reflective" umbrellas, and “shoot thru" umbrellas.
Reflective umbrellas can come in a variety of finishes. For instance, one that is finished in silver will provide a cooler light, as opposed to one that is finished in gold, which will provide a warmer light. So, decide what sort of finish would be best for the effect that you are trying to achieve. Reflective umbrellas provide incredibly diffused and subtle lighting effects for a beautiful soft glow, which is especially good for the skin of a portrait subject. If you don't have the particular reflective umbrella for your needs, here's an easy DIY guide to make your own reflective umbrella.
Shoot thru umbrellas, on the other hand, essentially function as oversized softboxes. The light provided by shoot thru umbrellas is a little less diffused than that of a reflective umbrella, but a little more than that of a softbox. Thus, they are a good compromise between the control and directionality of a softbox and the diffusion of a reflective umbrella.