Summarize:

In the user manual, you'll find a variety of user/installation instructions, including voltage requirements. Reading the user manual will also give you the dimensions of the hole you'll need to cut in which to place your lights. Installing beautiful recessed lighting may be all the rage, but if your circuit is overloaded, what use will they be for you? If you are taking out old fixtures and installing new ones, you can safely add lights that draw as much amperage (or less) as the previous ones. If you want to add more, consult an electrician. For example, if you had 6 fixtures, each with 100 watt lights, your circuit can hold at least 600 watts before hitting capacity. It is a good idea to lock the circuit breaker panel while you work so that no one else can turn on the circuit. Never work with circuits that are energized. Use the manufacturer's template or make your own by cutting out a circle of paper. Place the template against the ceiling in the desired location and trace around it with a pencil, marking the center point as well. If you want to place your lights according to a straight pattern or in a straight line, consider buying or renting a laser level. This will allow you to plot out the holes for the recessed lighting extremely straight. There's nothing wrong with looking more professional. Use a stud sensor or other type of structure sensing device to locate any possible obstacles in the area where you're planning to install.  If you have an attic or crawl space directly above the light fixtures, start by drilling a 1/4 inch (~6 mm) hole through the ceiling at the center point of each circle. Next, go into the attic and visually check for obstructions around each hole; you will need the light fixture to fit between the ceiling joists. If a finished area is above the ceiling, you can check for obstructions with a wire coat hanger. Bend a length of the coat hanger at 90 degrees about 3 inches (~8 cm) in. Insert the bent wire into each hole you drilled, rotating the bent portion around to check for obstructions. If the wire hits a joist, relocate your lighting fixtures accordingly.
Read the installation instructions. If possible, consult an electrician to determine how much voltage your circuit can reliably carry. Shut off the power before beginning any work. Mark out the location of each light. Check for obstructions in the ceiling.