What are some good methods or techniques to prevent a person's feet from getting sore when standing all day long, such as using a stand up desk at work, or people who have to stand in restaurants or shops all day for their jobs?
Besides changing posture as much as possible (fairly obvious and I imagine you want more specific advice), there's a great trick to rest your feet and legs throughout the week: when you sleep, put your feet up on a pillow. The rest you get every night will really make a difference during the day.
Check out the shoes other people are wearing in the same situation. Go for thick-soled, flat shoes. Running shoes may be the answer. If you have a strict dress code, get black ones, or use shoe paint to get them black. Wear thick sport socks, they do short ones. If it's hot they need to be ventilated. If it's very hot try Birkenstocks.
Most importantly your shoes have to fit properly, so they are comfortable all day. It's worth spending a bit more for this.
If you are standing rather than walking make the laces a bit looser. You can pull them tighter again to go home.
I used to work as a valet. Wear shoes that support your feet. Flat soles are terrible for comfort. You can put an insert into almost any shoe to make it relatively comfortable.
Additionally, lean against a wall or desk if possible. When standing up straight, the muscles in your feet and legs are constantly making tiny corrections to keep you upright. If you have something to lean on, most of those tiny corrections don't need to be done.
The following link also gives the suggestion of switching shoes in the middle of the day, so that the pressure gets shifted to different regions of your feet. http://deskhacks.com/best-shoes-for-standing-all-day/
Besides the problems with the muscles, as other users said, you should think about your veins. If your work connected with the standing on the feet all day, you should use: - compression underwear; - pills to strengthen veins; - gel for feet, special for veins.
Also, don't forget to put your feet above the rest body for a few minutes every day. It this should help to eliminate swelling.