Jacking the car at the back by putting the jack under the dif would be a bit hard if you've got a front wheeler. And if and when you do jack up the back put some blocks of wood or whatever in front of the wheels don't just rely on the reverse gear. Also when you but the jack stands under the car make sure they're on the designated lift points. The angle of the car shouldn't matter when the oil comes out because the sump plug is likely to be at the back (or really the side of the engine that faces the back) of the engine (it is on mine). You should be able to reach the oil filter from under the car. Don't forget to wipe a bit of oil on the rubber ring on the oil filter before you put the new filter back on.