In the graveyard, you do not want to step on or touch the grave of any person. This is rude at the least or it can cause them to become angry and visit you from the underworld. Another thing is that you should not wear sandals because this can cause the dirt of the graveyard to come home with them. The dirt of the graveyard in general holds energies of death and mourning and bringing that home can be bad luck.
You should never take dirt from a grave without paying for it, and even in that case you need to make sure the ghost of the grave is okay with you taking dirt from them because they may not want to help you in rituals. Stealing their dirt or trying to use dirt from their grave when they do not desire for you to, will cause the spirit to become angry with you and possibly begin attacking you. The ghosts of magicians will most likely be more understanding, but even then you should not take dirt from their graves lightly. Always leave a quarter for each handful you take from them.
It also goes without saying that you should not be disrespecting the dead while you are there. Assuming you are there during the day when there is less activity from ghosts and spirits, they can still hear you. Even outside the graveyard, it is quite possible you experience specters or apparitions manifesting in different ways. You may see vintage cars coming out of the graveyard at night, or people who look like they belong in a different era judging from their clothing. When this happens, do not interact unless you have a good reason.
Also keep in mind that if you go to the graveyard at night, you may see the god of death himself, his wife, his secretary, or some other shinigami. This does not mean you are marked to die yet, but they might just be politely asking you to leave or they might think you want to speak to them to provide offerings or requests. They can help you speak to dead ancestors or other people who passed on such as Nelson Mandela or Ho Chi Minh. The Shinigami are various and not all of them are known to have good intentions, but your ancestors should be protecting you before you go get so close to a deity.
You should not conduct a seance for a living person because this not only jinxes that person, but it causes an imposter spirit to go and play games with you pretending to be whoever. In religious organizations and cults who claim to be speaking to the ghost of a living person, you will notice they always say whatever the spirits know they want them to say, and cause them to look foolish in the eyes of everyone else. The easiest ghosts to interact with are your own ancestors and pets that passed on since they are waiting for you in the hereafter.