Cleaning in your socks!
Don't you injure your feet?!
I never knock on the door with kit in my hand, I think it's good PR not to appear as if you want to get out of there as quick as you can. I always go through the pleasantries, engage them in a bit of chat, accept a cuppa etc. I think it helps because customers are more willing to spend with you and recommend you if they like you on a personal level. I've even had customers trying to marry me off to their daughters!
Crossing the threshold... crikey, erm... at least 10 times setting up and 10 packing away, plus a few in between. With the machine outside the door, quite a few on a big job when it needs refilling/emptying and switching on and off a few times.
I don't understand the changing shoes thing at all! I simply pop a couple of sheets down as necessary, doubling over the one inside the door if it's a wet day. After I've finished I'll use a pair of overshoes if I need to pop back in over the hall carpet, and go back out to the door raking the carpet behind me.
When I'm doing upholstery and no carpet, I'll sheet the floor over with no shoes on, work, then take shoes off whilst removing sheets.
I always leave the machine outside unless I'm struggling for hose length, in which case it'll maybe need to stand in the hall blowing out the door for the first room, after which I'll back it outside. That is a bit of a pain in the bum regarding water though, have to only put a bucket full in first of all to avoid a hernia lifting it outside again!