You will never be actually seeing a spirit. You just know that it is there and a image is passed into your head by the spirit. You can contact them in many hundreds of ways, have you ever had a voice in your head that has saved you from doing something stupid? That is a spirit, most likey a Djinn. These are our "guardians". We are all spirits in a human experience, our body's are like cars and our spirit is the driver. Spirits often go into a what we know as a "life" to learn new things. If you really wish to be able to contact them then work on your 7 key chakras then the lesser chakras.
Other popular methods are through a Oujia Board, pendulum, scrying mirror, tarot cards, dice, crystals and many many more. If you want instructions on these go to my profile and look at the divination site or just google this subject.