Firstly, please make sure you are educated on the brow chakra, what it is, etc before working with it.
Secondly, your brow chakra is already 'open'. Chakras don't open and close, they are just either active or rather inactive. If you want to increase the activity of your brow chakra, try the mudra for that chakra.
Remember, don't work on one particular chakra. Keep them ALL balanced. Especially the brow, some people find it gives them a headache if it is over stimulated. Also, try wearing amethyst.
Third Eye/Brow Chakra info: http://www.eclecticenergies.com/chakras/introduction.php
Mudra (the technique to stimulate it):