The first thing (and most important thing) you should do when staining any wood surface is to get the suface as clean as possible. Stripping off old varnish or lacquer is the first step. Once this is done then you will need to sand the surface smooth and wipe down with mineral spirits. You can apply the stain now.
First off just vacuum your floor or sweep it to make sure you get the dirt off. Then just pour some Minwax into a rag and start rubbing into the floor. Make sure that you don't try to different spots at the same time and just focus one spot at a time.
If you use this product be aware that your wood floor must be of high quality , good condition and completely dry. The best situation would be if the floor was at least 10 years old. This product works great but tends look awful on wood which is young and not cured. It will enhance any blemish you have