The step you need to take when installing high hats or recessed cans is design a
layout. See our
How to Layout Recessed cans page. We will give you some tips
here and then provide you with some good links to sites that show step by step with
pictures and information.
The layout is critical in avoiding unnecessary damage to the ceiling and walls. Draw
your layout on paper first with measurements. You next need to know what the
ceiling structure is, where the rafters are. This can be done with a stud finder,
looking for the indents of the nails, by knocking on the ceiling with your knuckle or
in the case where there is an attic, just by looking.
Taking a pencil and ruler make a small  X at the center point on the ceiling of one of
your high hats in one corner of the room using your plan. Now check with a stud
finder to see if your recessed can will clear the ceiling rafters, if not adjust your
measurement so it does. Take the measurement for the next light and see if you are
clear of rafters there as well. In a typical design where you have say two rows. You
generally just need to mark out two lights to know if they are all good, but it
depends on the layout you choose.
After you draw your first circle using
the template provided with the high
hat, using a Sheetrock saw make a
slot starting in the middle. Using this
slot push the saw up at an angle in
both directions to make sure there
are no obstructions. Then in the
other direction do the same. It
should form a cross like in the
picture. The reason is if you do hit an
obstacle it is a lot easier to patch a
slot than a large round hole.
Links for installing High Hats or Recessed Cans

Do it Yourself Site
Lowes
Hardware Store - Has good pictures
Forte Electric
How to Install High Hats
or Recessed Lighting
How to Install High Hats
or Recessed Lighting
Smarthome, Inc.