When laying a laminate floor preparation is key.
The floor you intend to lay the laminate flooring on top
of must be dry, solid and 
level.
Sheets of fibre-board can be used to level minor deviations.
They also help keep the room warm and reduce noise from the
hard floor
Unleveled sub floors must be leveled out before laying the new floor.
Once you are ready to begin, the first step is the get rid of your old flooring. Whilst you can buy mouldings that go round the edge of the floor coving up the gaps, you will get a much better job if you remove the skirting / base boards and refit them after.
Before you do this make sure you can get a match otherwise you may have to replace them all. Also case should be taken when removing the skirting boards so that you won't have to do a lot of wall repairs later.
Pull up the carpet from the tack strips. Be careful working around the strips because they are very sharp and will rip into your skin if you scrape against them. Carefully, remove the strips with a claw hammer or similar because you do not want to damage your sub-floor too much.
If you are laying onto a wooden floorboards check the floor to ensure that it is stable. Nail or screw down any loose parts to prevent the floor squeaking.
If you are laying onto a concrete floor check for high spots. These can be chipped away with a bolster chisel. The simplest way to achieve a smooth surface is with leveling compound or screed. Simply mix this in a bucket with water, then pour and spread with a trowel. It will then set to a level finish. Make sure you allow several days for this to properly dry out.
Thoroughly vacuum and sweep the floor.
Do not use any water on the sub-floor.
Laying a laminate floor