My general rule when picking colors (usually two or three of them) for an outfit is to take them from opposite sides of the color wheel. For example, if I’m wearing three colors, I might choose purple, yellow, and green. Or I might pick orange, blue, and pink. This is also a good rule to help you pick out colors that don’t necessarily “match,” like red and seafoam green. Taking them from opposite sides of the color wheel will help balance out your outfit.
Less often I choose two or three colors from the same side… like orange and pink, or red and orange, or green and blue, etc.
Example from Pink Peonies (see blogroll)…
Disclaimer: I’m not necessarily a fashionista, so it may or may not be in your best interests to follow my advice in regard to personal style.