Make sure the floor surface is clean. Any dirty marks will be fixed in place with the stain. Check to make sure there are no other finishes on the floor, wax, varnish, glue, etc. will prevent the stain from taking and you will get an unstained spot.
Test the stain on a bit of spare floor timber, if you have some, to see how it looks when dried. The application method also varies how it looks so you may need to see the differences between using a brush, using a cloth and using whatever else is recommended on the stain. The number of coats of stain will darken the finish, that could include the number of times the brush goes over the same board while applying the stain the first time round.
Always apply the stain in the same direction as the wood grain and not across it.
Also if you are applying a varnish or wax over the top this could also affect the finished appearance and that will need testing and checking
Wear latex gloves as it will stain your fingers and open all the windows as the fumes will knock you out and will be flammable.
If you are using cloths to apply or to wipe up spills, brushes etc, don't throw them in the bin. Leave them out flat to fully dry, hung on a washing line maybe, before disposing of them as they can spontaineously combust. Otherwise store them in a sealed jam jar if you are going to reuse them.
I've never done a floor but have done furniture and would often have a test board of all the different methods of applying to see what it looks like.
Oh, work from the furthest point from the door and work towards your escape route. Ensure that you do not need to re enter too soon to close windows due to rain or going out as you don't want to walk on the floor until it is dry.
When dry don't tread dirt into the floor (socks or dust sheets only) until you have applied the varnish or wax finish.