The main thing to remember when taking digital photos are the basics. On cameras such as the one listed above the flash unit is mounted on the face of the camera. It is REALLY easy to have a finger in the way of this flash. When this happens, your photo will have a shadow cast across it. I can't tell you how many times I see "ghost" photos of a black mass in the corner of a haunted room and have to just roll my eyes...it's merely an object blocking the flash, making "shadowy figures" appear in the photos. I'm not saying that shadow people are never caught on film, or that real photo evidence of this kind does not exist, I'm just saying that very often it's just a user mistake with the camera that causes the shadow.
Also, while we are on the subject of the flash: The flash on these cameras (as I stated above) and on disposable or cheap 35mm cameras is located flat on the front of the camera. This can (and often will) cause things like "red eye". Your friend wasn't possessed, you just blew up his eyes with your flash. Also, if there is ANY dust or moisture or bugs or DARN NEAR ANYTHING in the air, you will get "orbs". Now, I know this is a delicate subject with most people, but the simple fact is this: 99% of all orb photos I have ever seen are very simple to explain. Real orb photos are quite rare, and you know them when you see them. Folks, haunted locations are quite often dusty from lack of use or disrepair. You will see this debris in your photos if you have stirred it up and caused it to become airborn. If you ever get a photo that you feel to be authentic, you should have someone who has experience with photos examine it, and give you their opinion. It's never bad to ask for someone else's opinion.
TECHNIQUES:
A very important thing is to be mindful of what you are taking photos of. I know you are in the dark, and it's hard to orient yourself. But so often I see people just waving their cameras randomly snapping off photos. When these people review their evidence all they are going to have are photos of the floor, or the ceiling, or a random corner...etc... You really should pay attention, make sure you are getting a photo of what you want to see. This will assure you that you have some reviewable evidence after the hunt increasing your chances of finding something.
A good technique to employ is to take photos in a series of 3. This gives you a comparative set. If evidence shows up in one of the photos but not the other two you get a good idea of when the evidence occured and gives you a good base for comparison. This also helps prove your point, because if it were user error such as a finger in front of the flash it would have more than likely occured in all three photos.
Also, keep in mind that you are around other people, and you are in the dark. When possible, try to warn others that you are about to flash. Blindness from the flash could lead to someone tripping. You always want to remain safety concious.
Another good tip is to make sure you carry enough batteries and storage media. You don't want to run out of either on an investigation. From past experience the one sure fire way to make phenomena appear is to not have a way to capture it. I have had so many things happen in the past JUST after my batteries died. I learned the hard way....always have a backup plan.
Expensive DSLR cameras are NICE, but not necessary on a hunt. In fact, I NEVER carry mine. a good 6-8 mega-pixel point and shoot is just fine. In the dark, possibilities for accidents increase. I don't know about you, but if I drop a camera I don't want it to be a $2,500 piece of equipment. Also, the focusing systems on the point and shoot cameras insures you to be able to get off your shot when needed. Sometimes, unless you are in manual focus mode, DSLR cameras will simply "hunt" with the focus and never make a connection. More often than not you will be standing in the dark listening to your lens try to focus while you should be documenting evidence. Sure, if you have good glass on a DSLR your images will be nicer, but for the purposes of a hunt a point and shoot or even a disposable camera are just fine. Anything else is just for show.