Depends on what you want the colours to be a part of. Are you mixing paint? Are you colour co-ordinating a wardrobe or house furnishings. Are you desgining a card or scrap book page. Are you piecing together fabrics for a quilts. Other than painting, a safe option is the 60:30:10 rule. Where you use 60% of one colour, add 30% of your second colour and then accessorize or accent this with 10% of the third color. Get paint swatches or colour card of each colour of your choice and place them next to one another and increase and decrease until you have a combination you are happy with.