I want to do a general service on my laptop.

If the laptop is fully functional, the only thing to do is to clean it.

KBDs are hard to clean if the keys allow debris to fall below them.

The Ventilation system is the most prone to dust build up.

Use compressed air on both.

The air must be very direct on the fan blades to get most dust off, but you need to also need to blow in from the intake vents. I would do that with the fans running, since that will help discharge the dust.

The any surface dirt on the KBD or screen is cleaned with a water dampened microfiber cloth then wipped dry with the other end of it. Just damp, so as not to have water getting into the unit.