So what you simply have to do, just as about any other skill or ability in the craft or other subjects, you have to have patience for it and practice in order to develop it and improve it.
What I recommend you is to use meditation in order to improve your third eye chakra. You need to dedicate time, effort, energy and patience in order to achieve improvement and development of this chakra.
Through performing a third eye meditation you can open your subtle senses to perceive higher-dimensional worlds and energies. The third eye is the center of what is called clairvoyant sight , meaning "clear vision," and refers to the higher-sense ability to intuitively see or perceive subtle energies.
Just dedicate some time to meditate and give it as much time and effort as you need in order to success.
You may search about opening your third eye in Google (or any other searching engine) and look for the sixth chakra (third eye) meditation methods. You will find a bunch of articles about it, and you will probably get the information you need.
I also agree that there are different methods of sensing and seeing spirits and other entities. You can also simply search for other plenty of various methods of sensing and seeing spirits and entities.