I've visited several salons run from cabins/spare bedrooms etc and these are my thoughts.
Consider all segments of your potential client base. By that I mean what suits a teenage market will not suit the more mature ladies, so play safe and choose a calm, neutral colour scheme. My walls are pure white which you might think would make the room cold and clinical. Not a bit of it! The floor is polished (real) wood in a rich chestnut colour, and that, combined with the colours of the products on show, ensures that the room is tranquil but not icy.
Consider the lighting, for both you AND your client. I have a daylight fluorescent fitting (sounds horrid, but isn't!) so that I can see what I'm doing (somehow I don't think a head torch would go down well during a Brazilian), but I also have a little desk lamp so that I can turn off the big light during a massage or a facial and have a bit of atmosphere.
As tempting as it is to have snowy white towels they are hugely impractical and will swiftly become battleship grey. My towels are chocolate brown - I do a lot of manually applied Fake Bakes, and they complement the floor perfectly.
Consider music. Your very favourite choons might be Marilyn Manson or Take That (perish the thought) but it's not there for your benefit; it's there for your client to be able to relax and drift away. For that reason I choose only instrumental music, so that clients are not tempted to sing along. It doesn't have to be classical music; I have some lovely ambient music by BlueTech.
Consider the temperature - you don't want it too hot or too cold. I have a heated couch which has proved a true winner with my clients. If you're lying still for any length of time you'll get cold very quickly, which makes it difficult to relax.
Your salon needs to look professional - not like a spare room with the guest bed shoved up to one end and a pasting table in the middle. It should look warm and inviting, aspirational but not opulent, but most of all it must be spotlessly clean!
Have fun choosing your decor - put yourself in the place of your client and you won't go far wrong!