I want to paint the interior of my house.
For each wall, I want to use different shades of the same colour. Please advise.
When you go to the paint store, look for the sample cards that have a single hue (or "color") at different lightness levels. Usually the lightest shade is at the top and the darkest shade is at the bottom of the card. Select the card that has the hue that you want to paint, but also take some similar cards back to your home so you can see how the colors look in in the room you want to paint.
Once you have chosen the card with the hues you want to paint, chose the shades you want to paint. Try not to pick shades that are directly next to each other on the sample card. Shades that are to similar on the small card will look even more similar on the large walls. This is because the visual system is not good at detecting changes in lightness for displays that are very large (see De Valois & De Valois, 1988).
Next, go to the paint store and have your paints mixed for you. When you go to do the actual painting, you can avoid getting paint on adjacent walls by taping up the side of the wall that you are not currently painting with masking tape to protect it. Be sure fresh paint is completely dry before putting masking tape on it. Also, be sure to wash your brush and/or rollers entirely before starting the next color to avoid mixing paints.
Not knowing the size of your house it's difficult to determine a color you can use. I'd suggest a warm color that you can balance throughout your house, starting maybe with a very light red in smaller rooms and darker shades in larger rooms. This color doesn't have to be red, but definitely use lighter shades in smaller rooms so as they appear bigger, and brighter or more passionate shades for bedrooms.