Trim removal and preparations
Sanding the floor
Applying Polyurethane floor finish
While preparing for refinishing your floor all you really need to do is remove all the furniture in the room. It's a better idea to remove any obstacles than rework around them. Then you can start the trim removal by removing the baseboards where the pieces are small. You can start by going at the trim at the edge with a pry bar and a hammer. Since the trim would be attached to the paint running a sharp knife along the edge would be another great idea. By continuing with this process and prying at the larger sections the trim would be done in sometime. While sanding the floor, using a good sander is very important. Also different woods require different kind of sanders. This must also be kept in mind. Before you start sanding, the room must be thoroughly vacuumed.
One you begin sanding most of the marks and scratches would vanish but the low ends and more resilient marks would stay. These would have to be worked away at with bigger sanders. Or you could use hand held sanders to concentrate on these marks and get through with them before applying the finish. Another glitch would be high spots or the areas where the floor would have absorbed moisture and risen above the level. This would have to be nailed in before moving further with the refinishing process. Edges can be tricky while sanding so they have to be handled carefully and with the right kind of equipment. They need a small sander which can be maneuvered around easily. While all the sanding is going on please also remember to change the grit with the different marks you encounter. Darker and more persistent marks have to be tackled with greater grit while the lighter and superficial ones can be dealt with the default 36 grit being used.
After all the sanding is done with, it's finally time to apply the finish. Before you even think of starting the job please get yourself a gas masks. The job is smelly and you would probably need those in due time.
When you start with the urethane the process of applying, it should always move with a wet edge. This means that it should move progressively towards one of the walls. While drawing your brush back make sure that you make a stroke to meet the stroke you made while applying the urethane. To get the best results try and stroke along the grain.
When all this has been taken care of your floor would look new and no one would ever be able to tell the difference.