Three important things to do when hand rendering plans (and elevations) are:
A layer color up by starting with a lighter marker color and adding multiple layers, this works far better than starting dark -trust me.
B always include shadows, not paying attention to windows or light-sources but by simply locating them consistently throughout drawing (all to the bottom/left for example).
C use a straight-edge made of matboard; cut the matboard in strips and use as an edge for the marker, this will keep lines straight and give greater control | while shown here for wood flooring this method can even be used for carpet, tile etc as a way to start a clean base layer.
This is straight from my book “Interior Design Visual Presentation” 4th edition.