Well, it's easier if you have a buddy that knows how to help you out the first time you do it.
This isn't a complete instruction set, i'm just writing some notes down here. The basic steps that I do are:
1) Run the car for a few seconds to warm up the oil, set up ramps (don't trust jacks) on a flat area, drive the car up and engage the e-brake.
2) unscrew the oil drain and drain out the old oil into a container. wait 10 min or so. Replace drain plug with a new washer.
3) unscrew the filter cap using the filter socket (it's cheaper to buy the ipd socket instead of Volvo's) and drain. clean the filter cap with a clean, dustless rag, replace the rubber grommet on the filter cap. Insert a new cartridge and put a little fresh oil over the edges of the filter cartridge, and reinstall the oil filter.
4) pop the hood and fill it up with clean oil, and fill to recommendation based on a new filter (if you didn't change the filter, add less oil). Check with dipstick.
5) Run the car for a few minutes, then check underneath for any leaks. If no leaks, you're done.