Metallic or iridescent acrylic paints (and micas) can be used in the same way as any other acrylic paints.
Each person has his or her own favourite brand of paints. Every brand acts a bit differently from the others, so keep looking until you find one you like. Combining different paints can create appealing results; too, they can react with each other and give an effect that you would otherwise find by sticking to the same brand.
Some of the good metallic lines are FolkArt and DecoArt, of which I use both plus other brands. You will just need to play with them and see which is better for the purpose you require. Just remember experimenting is always a good way to go as this is the way you will stumble upon something new.
If you have mica powders, it is possible to make your own metallic or iridescent paints from them. Just mix a little powder with a squirt or two of water (or any other polymer clay-friendly medium of your choice) until you reach the desired consistency. This can then be painted onto your baked clay to add a wonderful effect. Using the pearl mica powders over painted areas will give a very unique pearl effect that will only be seen as you move the object to catch the light.