There are many third eye spells, to open up your ancient powers. Others have advised correctly, balance is very important. In which way do you want to focus this second sight? Auras? Precognitive visions? Dreams? Spirit appearing? To find the best suited spell evaluate your goals and then search in those areas. Using crystals may help align the Chakras as well. Drinking Teas for visions, such as Mugwort may also help. Mediation, and a lot of it. Patience. If you are trying to extend your own natural senses, then try using them more. Listen to as much as you can hear, beyond the cars beyond the trees, and just listen. Then once you have mastered this look, look in the spaces between the trees and clouds, see the movement of the energy the electric particles that make up the Ether. See the variations in color of the auras, start with looking at plants with the sky as the background, and see the bands of color. Stare into the dark and see the shapes. Feel the surface of everything, the velvet of the sage leaf, the smoothness of a stone polished by the river, and the grainy texture of wet sand. Really feel it. When you strengthen the senses you already have you strengthen the sixth senses as well.
Blessed Be All Who Use the Magick of the Gods.