Eventually this is likely to happen to all of us. If you have kids, pets, ghosts or you are unlucky and uncoordinated by nature. Assuming that after the spill you don't see smoke, or hear the laptops death crys, the first things to do immediately after the spill that may help you avoid a costly computer fix is:
Power off the laptop - try not to move it yet.
Soak up the remaining liquid.
Unplug all devices from the laptop.
Remove the battery from the laptop without tilting the laptop if possible.
If water is what was spilled, then you may be able to simply allow the laptop to sit under a fan for a day. If you're the patient type. If sticky beverages like coffee and soda is to blame then you will most likely have to open up the case and clean inside.
Removing the laptop case can be a bit tougher than you may realize so make sure to get directions from the manufacturers website and take notes or pictures as you progress along with disassembly and reassembly.
Be sure to remove components from inside the case and inspect them as necessary; hard drive, RAM, cd/dvd drive, keyboard. The keyboard is notorious for not being the same after something is spilled on it. It may be unrepairable but it's generally the least costly part to replace. You should only clean electronic equipment with denatured alcohol which can be purchased for about $5 a liter. Allow all parts to dry before reassembly. Good luck and back up your data next time!