I agree with all of the points that MarkT made, except this one:
MarkT:
Drain Source Voltage Vds:
This is basically the voltage rating of the MOSFET. When the MOSFET is turned off, the whole supply voltage will be measurable across it, so you must not exceed this value.Ensure this rating is twice your supply voltage if you want reliable operation. Rapid switching can cause spikes of twice the supply voltage via stray inductance very easily.
You don't need a rating of twice the supply voltage, just a rating comfortably in excess of the supply voltage. If you are switching an inductive load, you will use a flyback diode across it to catch the back emf. If you are switching a non-inductive load, then a power mosfet will easily absorb the small amount of energy stored in the stray inductance (look for "avalanche rating" on the data sheet), unless you are switching very high currents and are very careless in your circuit layout (in which case you will have other problems anyway).