Start your refinishing project by removing every item from the room in which you'll be working. This means furniture, rugs, decorative items, fixtures, etc. There will be a large amount of dust in this room, during sanding, and anything left inside will be exposed to the dust and debris.
You will also want to seal off the room as much as possible so that dust doesn't spread throughout your house. Cover the room's doorways, vents and electrical outlets with plastic sheeting and use masking tape to fasten the sheeting in place. Every opening should be closed or covered to avoid spreading dust throughout your home. Open windows in the room to ventilate and remove some of the dust and residue that will be in the air.
Check the floor for any nails or, if you pulled up the carpet, check for any carpet staples or tacks that may have been left behind. Sharp objects such as these can destroy the sandpaper on a sander, forcing you to change it out, making the job longer than it needs to be. Using a hammer or nail setter, pound any nails you find as far below the surface of the floor as you can get them. Remember that your floor's surface will be a little bit lower than it was, after you've sanded, and you could potentially sand down to a shallow nail. Thoroughly sweep and mop the floor before starting any of the work.