You can use a website like Adobe Kuler to see what complementary colors are
I was recently reading Picture Perfect Practice by Roberto-Valenzuela. In his book he suggests that really good photos will comprise of no more than three colors.
When it’s impossible to get those kind of color matches when shooting a photo you can use a technique like this to fix the problem. In this video by Aaron Nace of Phlearn you’ll learn the secrets to doing this quickly and easily.