One problem with hardwood floors is that they scratch and the scratches have a tendency to get deeper over time.
I don't have a hardwood floor anymore, but I used to. I do however, still have hardwood bannisters and they have the issue...scratches.
A nice simple fix is to find a crayon in a similar color. Or you can buy one of those special wax crayons that are for this purpose...but I find a regular kids crayon works just as well.
Soften the crayon in the microwave and use the softened crayon wax to fill the scratch. Then using a butter knife or credit card, smooth it out to level with the rest of the floor (or bannister) surface
You might have to soften the crayon a few times to fill your scratch, but when you are done, you have filled the scratch and leveled it out.
If you are having trouble filling the scratch then grab a hairdryer and use it to soften the crayon as your squish it into the scratch.
Once you're done, simply it buff the area...and you should be good for a while.