Here is a tip that helps bring a lot of depth and quality to my props: basecoat colors.
Depending on the color you want, basecoat appropriately to bring out the subtle tones in you prop. Here are some examples:
Painting to look like steel: basecoat blue, then silver, then add touches of brown
Painting gold: basecoat brown or red (depending on the tone you want) then add touches of brown to weather
Painting leather: paint white, then alternate light and dark brown and stipple it on to create a leather effect.

Keep building and have fun!