1. Pick a blade size
Saw blades are extremely expensive - the fewer of them you buy, the happier your wallet will be. If you plan on getting a miter saw, table saw, a radial arm saw, or some combination of these saws, pick a blade size and stick with it. While there are a variety of sizes available, the most common and popular sizes are 12" and 10". If you stay with the same blade size for all of your different types of saws, you'll be able to share saw blades between your saws. In the long run, this will save you a lot of money.
2. Cordless or corded
Batteries for cordless tools have made remarkable advancements during the course of the last several years. Tools that you would never think would have a cordless option, such as circular and miter saws, now offer cordless models. If you are thinking about getting a cordless saw and you have, or may someday have, other cordless tools, think about sticking with a single battery/manufacturer system -- that way you can use batteries between your tools. Extra batteries are extremely expensive -- it's often cheaper to buy a brand new tool than to buy replacement batteries. If you purchase several tools from the same manufacturer using interchangeable battery systems, you'll have extra batteries available to finish your job, this can significantly increase the amount of work you can complete.
Before deciding to get a cordless saw, remember that even though cordless technology is very advanced today, there will be limits to the amount of work that can be completed in a single session with a cordless saw. If you're a hobbyist or you don't use your saw for extended periods of time, a cordless saw may be a good solution for you. But if you are a contractor the type who will be sawing all day long, you will probably want to bypass cordless technology for saws that draw excessive amounts of power when cutting.
Battery operated saws are also more costly to purchase and to maintain. Your cordless saw may last for 10 or 20 years; but you'll be lucky if the batteries last for two. On top of the steeper cost up-front of a cordless saw, you can plan on shelling out more money in the future too as the batteries will need to be replaced eventually.
3. Do your reading before you buy
Saws are a big investment -- they are expensive and they get a lot of use in the typical workshop. Buying the right saw is important and even more important is to avoid getting a saw that doesn't work for you. Prior to buying a saw, surf the web for reviews, rankings, and opinions for the type of saw you are thinking about purchasing. If you use a saw for a week or so, you will form an opinion about it. But it is almost impossible to get a real feel for a saw just by studying the specifications. When you read the internet for saw reviews and rankings, you'll be getting the opinions of people who have worked with the saw and who have an informed opinion. If people have problems with their expensive new purchases, they are usually more than happy to let other people know if something is not good. Let their bad luck save you from getting stuck with the same bad saw.
Before getting a saw, read the user manual. You can learn a lot about how easy a saw is to use by reading the manual. If it takes a whole bunch steps and an iterative process to make sure that the table and blade are square, you can be sure that this will lead to frustration in your future. If you are thinking about a saw with several cutting configurations, look at the user manual to find out what level of effort is needed to alter the cutting configuration. If the set up is difficult and hard to understand, it may be more trouble than it is worth and you will be inclined to just not use your saw this way. Even though your saw has some neat features, if they are too hard to use, you won't use them. So why fork out the money for them? You can discover a lot of these sorts of issues just buy reading the manual before you purchase it.