Just to build on what richardtallent said...
3/4 inch solid oak floors can handle 3 refinishes we were told. Beyond 3 and the wood is to thin.
This is very very dirty work. the dust will get everywhere. When we did out first floor, we had just remodeled the kitchen. make sure you tape off any rooms you want to keep clean with heavy plastic and painters tape.
Tape up any heat registers and returns. change your furnace filter (if you have a furnace) before and after. If you're doing this while you need the furnace (summer or winter), check the filter during the process.
We did 3 passes on ours (they had never been refinished and were original to the house) from course to medium and finally fine. Ours was a complete gut, so we didn't have to get around floor molding, we replaced it with new stuff afterwards. Orbital sanders (the one you stand to use) are powerful. If you use belt sanders you can go with the grain producing a better product.
Watch for popped nail heads. Sink them when you can. They eat sand paper.
Fill in any gaps with wood filler to match the floor. Stain will stick to it and the poly will protect it. Major flaws in the floor should be fixed. Even though my house is over 80 years old, lumber liquidators still sold the oak wood.
Keep the work area clean and vacumed. We used an everyday shopvac, and it had to be cleaned constantly.
We used belt sanders and did it by hand on our hands and knees. A lot more work but allows for much finer control. If you're not paying attention, you'll gouge the floor. Feel the floor with your hands as you work. There will be so much dust on it, you won't see it with your eyes. Good wrap-around eye protection, too. You'll cry saw dust at the end of the day.
Two coats of stain, waiting a day in between and two coats of poly (minwax) waiting a full seven days in-between. The fumes are amazing. Get some fans to help circulate the air. If you insist on sleeping in the house when the poly dries, do not step on the floors for at least 24 hours after each coat, and be careful for the next 24 hours. Our front door is feet from the stairs to the 2nd floor, so we set up a plank to get out of the house for work.
Tack clothes are your friend; use them between each pass of staining and poly.
Make sure the place is spotless while staining and poly; we made two passes each time we stained or poly (there were four of us working on the floors at the same time).
It's a lot of hard work. Get a good mask, not the crap paper ones. Keep the windows open and blast the music.
I'd go out for a smoke and you could just see saw dust pouring out of the windows. It will get everywhere. Clean the walls, the ceiling. Then clean them again.
Every aspect of this is finish work, even the sanding. each step will determine how good the next comes out. Take your time.