If you kneel down (kneel on something so you're not on the floor) and look along the bottom of the door, you should see some slotted holes, poke some stiff wire or similar in the hole and move it around, you might first of all get a little debris, but then the water in the door should start running out. Most doors should have drain holes, as well as the the boot (trunk) lid. Probably worth doing them all.
If you look under the bonnet (hood), on either side near the hinges/inner wings/bulkhead, you may also find some drain holes for the area under the windscreen. If these are there, check them too.