What you may Encounter:

There are generally 2 types of spirits you may encounter. One was a human at one time and it has remained on this level for some reason. It may not know it's dead, may be held here by unfinished business, guilt, etc. These spirits are like the person was when they were alive, so they could be good or bad, just like the living, but not normally dangerous. This human spirit is the type you will encounter 95% of the time. You could also witness a residual haunting which is just a playback of a past event. This is just like watching a video from the past playing over and over. The other type of spirit you may encounter were never human and are generally bad news. You must be aware of this type but not obsessed with them, the chances that you will encounter them in a regular ghost hunt are slim.
So be aware and protect yourself and you should have no problem.