Technique above sounds good to me.
Few more tips, remember to take off all rings, watches etc. Seen a screen chipped on the final whacks home.
Warming the rubber first can also help, put it on a radiator or give it a warm up with a hair dryer. Don't soak it in hot water as you'll trap the water under the seal and the window apature will start to rot
Also a lot of people reccomend washing up liquid as a lubricant, for christ sake DON'T do this. It perishes the rubber and attacks the metalwork.
We use plain old general purpose grease. Just slap it round the window apature. Careful not to get it on the headliner. Helps the rubber slide in, gets a good seal and repels moisture.
We also found it slightly easier to work top to bottom.
And don't buy cheap seals!