Assuming your using a floor edger and 220 belt sander, you would
Depending on how old the finish is, we use 40 grit next we use 80 grit on both edger and belt machines. End with 100 or 120 on the big machine(belt). You can climb the grit ladder more closely if you want to ensure a perfect job. EX.-40,50,80,100
We then scrape the corners and finish them off with the RO90 delta.
Then we RO150 all the spots that we used the edger on.
Lastly we buff the floor with 120.
The biggest tip I can give you is, with dark stain, you should waterpop the floor prior to staining. This will re-open the pores and allow the floor to accept more stain. But more importantly it will remove any buffer swirls and give the stain an even look. It will blend all the edges and hide many errors that might not have been seen during buffing. After sanding use a mop or wet rags and wipe water all over the floor. Dont soak it but def. get the wood wet. Let it dry before applying the stain. Just trust me on this.
Dont use minwax slow drying stains. Instead use the new stuff that dries quicker. Lowes and HD both carry fast drying stains now. They will look the same and will dry overnight.
As usual samples are your best bet.
We buff the stain on with a carpet pad cut to the buffer size. We remove with terry cloths placed under the buffer. This will speed things up and save your back.
If you've never done this before I would HIGHLY recommend getting someone who has to help. Or go Natural. A dark stain is the hardest floor to do IMO.
Feel free to IM me any questions you might have.
Here is some examples of our traditional stain jobs
http://www.flickr.com/photos/ecooptions/sets/72157627719885035/
