Laminate flooring is made with a tongue-and-groove mechanism that snaps together. While the usual way to install it is with the tongue side of each board facing out so that you can snap the groove of the next board onto it, you can just as easily install it the other way. This makes it easy to extend the floor through a doorway into another room. You'll have to cut the flooring to fit around the door jamb, and you should do this with care. Any chips or irregularities will be visible.
Lay out the flooring for three days to allow it to acclimate to the conditions.
Remove skirting boards from the walls, if there are any, by prying them off with a hammer, and remove the doors hanging between the two rooms by tapping out the hinge pins.
Lay a moisture barrier over the subfloor and staple it down. Use a section of flooring as a reference to cut the bottoms of the door jambs so they will be above the level of the floor. It will be easier to make this adjustment, and to lay the floor, if you can remove the jambs, but if not, cut them in place with a hand saw.
Doorway perpendicular to flooring direction
Start laying the flooring against the wall in one room, leaving a gap of 6 mm (1/4 inch) between the floor and the wall. Click the ends of the boards together and cut the last board to fit with a circular saw. The tongues of the boards should be facing away from the wall.
Lay the flooring, staggering the ends of the boards by at least 15 cm (6 inches) and clicking the boards lengthwise onto the ones next to them. Tap the boards together end-to-end with a tapping block. When you reach the end of a course, pry or tap the last board into place with a pull bar.
Notch the board that extends through the doorway with a jigsaw and click it into position. Extend the course of flooring that connects to this board to the far wall of the next room. Continue laying the floor until you reach the other side of the doorway, then notch a board to fit around the door frame.
Measure the notch from the framing behind the jamb rather than from the jamb itself. When you have cut the notch, pry the jamb away from the frame so you can slide the board down behind it, then tap the board in place and replace the jamb. Continue laying the floor in both rooms to the far wall.
Go back to the doorway and finish the installation by laying the floor in the opposite direction. You will be fitting tongues into grooves rather than the other way around, but this won't be any more difficult.
Doorway parallel to flooring direction
Start laying the floor against the wall in one room farthest from the door and continue the installation until you have installed the second-last course.
Cut the boards of the last course to fit in the gap between the floor and the wall with a circular saw, leaving a 6 mm (1/4 inch) gap, but don't cut the section that extends through the door. There will be a tongue on this section that extends through the door.
Measure the distance from this tongue to the edge of the doorway with a measuring tape, and if it is more than a section-width, cut another piece of flooring to fit in the doorway.
Measure the distance from the tongue to the edge of the doorway and cut this amount off the groove-side of the first course of flooring that you will lay in the next room, leaving a notch for the door. Lay the first course in place, clipping together the sections that meet in the doorway.
Continue the installation to the far wall.
Slide the flooring under the door jambs. If you notch around the jambs, the gap will be visible and you will have to caulk or otherwise hide it. Replace the skirting boards or install new ones after the floor is installed. They are necessary to keep the floor down.
Wear safety glasses when cutting laminate flooring. The sawdust is full of plastic and fibreboard particles that can damage your eyes.