I'm sure there are plenty of ways of doing this, but this how I go about it....
Putting a bike back on the road after it's been standing for many years comes with some obstacles. One of which being seized up and rusted out forks. Seals that have been in so long that they've almost bonded to the metal and are solid.
With the bike held securely on a stand (or pivoted using the centre stand and swing arm - per another tips page), remove the front wheel, caliper and guard to allow the stanchion to slide out under the bottom clamp when you get to loosen off the clamp bolts later on.
While the forks are still bolted tight in the clamps, loosen off the fork top nuts (some models) or remove the circlips in later models, making sure the spring doesn't ping the plug up in the air. If you don't loosen these off at this stage then you will need to find a way of clamping the stanchions in a vice later on to try to get these things out. I also loosen the two fork drain screws at this time, again as it's easier when they are being securely held.
Next I remove the forks from the bike, dropping them down through the clamps. Then drain the majority of the oil out of the top of each fork into bucket. I remove the spring and any spacers, then invert the fork over the bucket, remove the drain screw and let it stand while the remaining oil comes out.
Once the oil has drained out, you'll need to remove the chrome stanchion which means removing the allun bolt at wheel end of the fork. For this you will need to clamp the stanchion to stop it rotating.
If the stanchions are beyond repair then holding them in the main vice isn't such and issue, but if they are good enough to use or to get re chromed then they could be ruined by using a metal vice. I've got some rubber jaws on my bench vice which does the trick. Sometimes the allun bolt comes out just by having the sanctions held, but not always, and may need some extra work.
What I've done on a few occasion, is find a piece of wood (old broom handle or even an old cricket stump are about the right size) then taper one end and hammer this into the stanchion. Then clamp the wood into a vice and this usually does allows enough grip to progress the job. I also use a butane torch to heat up the fork end around the allun bolt and with the wooden stump held in the vice the allun screw usually comes out pretty easily.
So far I've only had one where it was so bad that the above hasn't worked and I've then had to drill it out. I suspect that was really more due to a previous owner having messed up the head of the bolt and being unable to get sufficient grip than anything else.
Next remove the seal retainers and put the fork bottom in the vice, carefully clamps so as to not scratch the allow. Then use the gas torch on the old seals for a good few minutes until they are smoking, this breaks the bond between the old seals and the allow. Then use a large screwdriver or something of similar size to gently prize out the seal, without damaging the alloy.
Clean up the fork internals around where the seals were located to allow new ones to be fitted. Check the rest of the forks and internals for signs of wear or other issues before starting to reassemble.
Put the new seal on top of the fork mouth (making sure you have it the right way up!) and gently push by hand the get it in as far as you can. You can then use a seal driver (or if you've not got one then it's possible to use the old seal if it wasn't badly damaged in the removal process) and use a rubber hammer to fit the new seal. Repeat for the 2nd fork.
Reassemble and fill with new oil.