Door cards are easy when you know what to look for:

Use a plastic pry tool to pop off the speaker grilles on the door, as well as whichever trim you have covering your door handle.
Next, find the 3 T25bolts that fasten the door card to the door.
You can now start prying the card off of the door- the best way is pushing 'up' into the bottom of the first few inches of the card until you hear a small 'pop'; this is one of the plastic door locks popping open. Then you can pry from the bottom up, all the way around the door card.
The top of your door card will need to be lifted straight up, as it is hooked over the bottom of the window frame.
When you put the card back on, you will need to first make sure all of the plastic locks (circular vertical pieces of plastic sticking out of the back of the door card) are pulled up into the 'open' position. You will hear them pop back closed when they lock back into place when you push the door card back on.
Finally, mind the cable that slides in/out of your inner door handle. It is easy to put back into place, but if you forget to do so, you'll have to pry the whole thing off again. Depending on your car, you'll have either one or 2 electrical connectors that are easy to disconnect from the card, but don't always seat perfectly when you pop it it back on. Make sure your power window is working prior to getting the door card snapped back on and bolted in.
(I've done this well over a dozen times now, with many of those times to fix one of the above errors...)