Most Helpful Guy
Colour wheels. Colours opposite each other in a colour wheel usually highlight or compliment one another. Or you can just see what shades would work well. Go for the most common colours if you don't trust your sense yet, and as you get more comfortable you can experiment more.
Most Helpful Girl
Why do they need to match? But if you want them to focus on the colour wheel, neighbouring colours they usually work, or there's cold colours (blues, greens) and warm colours (reds, yellows). You could always choose monochrome but that can be a bit samey. Or black, white and grey and just add a pop of colour in the form of a scarf, shoes or other accessories.