You could read 1000 different trip reports and have a trip that is completely different. Monkeeman is right, different for each person, setting, amount consumed, type of music. Also if someone is having a bad trip it tends to bring everyone down.
In My Opinion the one thing to really make sure is, its all in your head. If you think you are going to have a wierd or bad trip, then you probably will. Go into the trip happy, excited, open to all, and make sure you dont have any serious problems in your life that are going to be on your mind.
Also, from having a bad trip there are many ways to get out of it and the main thing is you just need to get your mind off of the negative shit. I've had friends freak out, mainly on acid but some on shrooms, and nice mellow music can help but it can be too much for them too. The best thing that I've noticed to work is chronic, not the actual smoking, helps but, if you have really really good greenery with a nice potent smell, just have yourself or whoevers having a bad trip, to just close their eyes (momentarily cause that can cause some different crazy hallucinations) and take the biggest sniff of the bag. Deep and slow and tell them to think about what they're smelling. Will probably make them FIEND to smoke but it has always worked at getting peoples minds off of the bad and think about something they will always love. Ganja