Me and my sis have these issues too, she works at a Pharmacy and is on her feet for 8 hours everyday and when I do my part time Manhattan make up freelancing it's 8 hours straight too, such a pain in the bum (I mean feet
)!
I agree with others, comfy shoes (if that's possible), lots of food that gives you energy, lots of water...and mandatory feet baths when you get home
There is another thing that helps, don't ask me why it helps, but it does, every one I know who have to stand a lot are doing this:
take Magnesium pills. Here you can get them in form of those pills that disolve in a glass of water, but I'm sure you can get them in a normal pill form as well. One glass a day and it'll soon start to show.