Start by labeling points of interest where a light should be. For example, stove tops and sinks could use overhead lighting in a kitchen. If you have no focal point, just put your first can light in the center of the room.
Divide the height of the room by 2 and use that number as a guideline for how far apart the lights should be placed. An 8-foot ceiling should have 4-foot spaces in between lights.
Keep your recessed lights about 3 feet from the wall to avoid shadows. These make the ceiling appear lower whereas lights reflecting off the wall give the space a brighter, larger feel.