For our purposes, the two main types of router configurations I will discuss are 1) table and 2) portable. For edging small parts, the table router is convenient. When a part or assembly is or becomes too large, a portable router will be required.
It's all about speed. Spindle speed and surface speed.
For best results, routers should have a minimum no-load spindle speed of 10,000 rpm. Higher speeds of 20,000 to 25,000 rpm are desirable and should be used when possible. Slower spindle speed routers are available and by modifying the types cutters they will also produce good results. But as a general rule, stick with the higher speed routers.
Surface speed refers to how fast the outer edge of the router bit is travelling. A good everyday example of surface speed is a ceiling fan. The outer edge of a fan's blade travels much faster than the the section closest to the center. Another example is a dentist drill with very small diameter tools. To achieve the necessary surface speed, the dentist drill requires very high spindle speeds. They are usually air powered which gives off that lovely sound we all enjoy.
Flutes and shanks. Double or triple straight-fluted cutters 5⁄16 to 1⁄2 inches in diameter will produce good cuts. Smaller diameter cutters should be used with care. If cutters larger than 1⁄2 inch in diameter are used, the material should be machine-fed rather than hand-fed to overcome chatter. For safety, cutter shanks should be as large as cutters in diameter. Single-fluted cutters should not be used under any circumstances.
Steel router bits will produce an excellent initial cut, but carbide bits can give a comparable cut and will give many times longer life. As I mentioned above, the spindle speed required to produce a satisfactory edge is 10,000 to 20,000 rpm. A smooth, constant feed rate of 10 to 25 feet per minute is required to prevent localized heat buildup. Too much heat will cause smearing or gumming of the cut edge.
Low-horsepower (1 hp or less) routers should not be used. They tend to bind on the material and will remove chunks instead of a smooth edge. Avoid using router bits less than 5⁄16 inches in diameter because smaller diameter bits tend to clog and break. Routers are prolific chip makers. Use a router setup that will effectively remove chips. This can be as simple as friend with a shop vacuum or a built in collector as part of your table router.
All cutters should be kept sharp and should have a back clearance of about 10 degrees and a positive rake angle of up to 15 degrees. If these terms are unfamiliar to you, buy your cutters from a well resourced wood worker's supply store. The staff can help you select the right ones.
I cannot emphasize enough the importance of safety glasses when using a router. It is very easy to apply enough pressure to shatter cutters and at those high speeds bad outcomes are very likely.
This is a summary of routing. An entire collection of articles can be written regarding this topic covering everything from technique to tool selection. Visit a local wood worker supply shop and talk with the staff. They are a great resource.