The basic rules for combining colors and multicolor patterns are simple. The only thing to remember is when you have a pattern containing multiple colors you should only try to match one color in the pattern.
If the pattern contains red, yellow and orange, then select one of those colors and match it with a shade of the same color. Sometimes, the multicolored pattern will have a color more strongly represented, and in that case, the strongest color in the pattern should be the one used to matching.
You should never use multiple patterns together. There are current schools of thought regarding fashion that say it's okay to combine different types of stripe, or plaids with stripes or patterns. However, I, personally, have never seen an example of this that was appealing. The problem becomes especially significant when you deal with persons who aren't model thin.
See also: Color matching