-Make sure you have extra batteries and the batteries are brand new. Ghosts tend to suck the power from electronic devices.
-Make sure you have a good camera. A disposable camera will work, but the pictures won't come out as good. Also a digital camera can be useful at times, but can sometimes suck too. They're good because you can see the picture right after you take it and you can delete it, but you don't get any negatives to prove that you didn't alter the pictures in any way.
-Talk to the ghosts. Get them to come out in the open. Enter the room and say something like "Hey my name is ________ and me and my group here are taking pictures on our paranormal investigation. We were wondering if maybe you could pose for some." Trust me it helps.
-Try to avoid any shiny surfaces and know where all the lights are in the room so not to confuse them with an orb or apparation later.
-Ghosts follow people. Don't just take pictures of the walls and of objects and things, but add people to some pictures. Because it is more likely that something will show up in a picture with people in it and besides if nothing else shows up then at least you have a good picture of some friends.
-Don't just walk into a room and start snapping pictures. Like I said talk to them, but also just stand or sit in there completely silent for a few moments to let them get used to you.
-Make sure your lense it clean and nothing like hair or a camera strap is in the way because it can look like something ghostly. I have some examples of how these can look on my picture page.
-Always remember that not all paranormal phenomena shows up on film and that it is better to take pictures at night with a flash.
-Don't be afraid to take more than enough pictures! What if nothing shows up except on the 67th picture?
-Try not to take pictures when there is a lot of moisture or dust in the air, it can look strange but sometimes it's just fog or moisture on the lens.
-When the air is cold and you can see your breath try not to breathe while taking a photo because it can be mistaken for an apparation.
-Ghost energy is usually caught on film about 2-10 ft. from the ground, but don't just take pictures of the ceiling.
-The chances you will see an evil spirit are slim to none, but DO NOT dare an evil spirit to come out for a picture.
-Good luck with the pictures!