1. carefully sand the floor.
2.hoover up and wipe away all sawdust and dust.
3. wipe of the floorboards with a damp cloth.
4. stain the floor boards with the appropriate colour of wood stain

Pretty much. Be prepared for a LOT of dust. Seal every adjoining room off
(you'll still find dust in the most bizarre of places). Knock any
protruding nails down with a nail punch. Work diagonally with the big
sander then do the edges. You might want to consider cleaning the
floorboards with white spirits or a proprietary cleaner - if you use a damp
cloth make sure the floor is bone dry before varnishing. The floor is
particularly vulnerable until you've varnished it so careful with
footprints, spills etc. once you've sanded it. If you want a light colour,
consider a clear varnish - it's amazing how dark the natural wood will
appear once varnished. If in doubt test a small unseen area first. Hope
this helps!

Andy