How much do I want to spend?
The performance of a scope - like most other optical products - is heavily tied to the cost. Know how much you're willing to spend as spotting scopes range from $350 to $6000 without a tripod. There is a noticeable quality difference every time you step up a level. For example a $1000 scope will offer a significantly clearer, sharper image than a $300 scope. More expensive scopes will often have wider viewing angling and come with other features like a dual speed focuser and weatherproofing.
Objective lens size
This determines brightness of the image and size of the scope. For viewing distance objects from your deck, a 80mm or 100mm is going to be what you want. For hunting or bird watching, you may want to consider something in the 60mm range for better portability.
Many of the better spotting scopes allow the mounting of external cameras via an adapter: this is known as digiscoping (a portmanteau of digital camera and spotting scope). Digiscoping will give your camera magnification beyond that of a telephoto lens without the burden of carrying one in the field.
Digiscoping is an extremely large subject and if you need further advice please don't hesitate to contact us.
What sort of tripod should I get?
Any tripod with a video-head is suitable, you can also have a look at our tripods for spotting scopes collection.