First off I'd like to point out that there is a significant difference between a graveyard and a cemetery (one has a church attatched and the ground is hallowed the other is just a patch of dirt with a bunch of corpses in the ground)
Now that we've defined a graveyard, lets get into working in them
Tools needed;
Pendulum and/or dowsing rod
Divination cards
Hand shovel
Spray bottle full of Holy Water
Scrub brush
A minimum of 6 pre 1982 pennies but best to bring at a minimum of double that.
Candy that is safe for small children
Cigarettes or Cigars
Dark liquor
The gate - When you get to the gate get your pendulum out and request permission to enter from the gatekeeper of the graveyard. If you receive a yes on your request (which most of the time you will) place 3 of the copper coins at the entrance of the gate upon entering, that is paying your way into the spirit realm.
If done properly the graveyard will feel cold and devoid of feeling upon entering. You will be able to tell you're not in the same place you were in before, although it will look the same, it will feel a bit dreary or gloomy but also very peaceful. It is also very possible that you will feel incredibly cold, like shivering cold so dress warm even if it's summer time.
Upon entering you must find two things.
PAY VERY CAREFUL ATTENTION TO ONLY WALK IN THE DESIGNATED ROWS AND NOT OVER THE TOP OF PEOPLES RESTING PLACES!
You will need to find the oldest grave in the plot and the youngest grave in the plot. Oldest is by numeric date or the oldest looking stone you can find in the plot. (only use appearance if you cannot make out the writings on the stone) Some stones go back into the 1800's or farther back depending on the location so reading them may be hard.
Youngest is the shortest lifespan you can find. In otherwords the grave of a child.
You will leave the cigars or cigarettes at the oldest grave, and the candy at the youngest grave for the spirits that occupy the ground below the stones.
Also at the oldest grave you will leave the liquor, specifically for the Baron to pay your respects to him in his domain. It is advisable to request his protection while you're visiting his space and ask that you not be mislead on your journey in his lands.
Now the fun begins. Take out your pendulum or dowsing rod and ask it to show you the location of a headstone that belongs to a spirit that would be willing to work with you. This may take a while, when you find the stone it's time to make a friend, but never presume upon a new relationship. That's not something you do with someone you just met, you don't do that with a spirit you just contacted either. When you find the stone, you may use either the pendulum, the cards or a combination of the two to establish communication, and terms (essentially you don't ask for anything the first time you visit the stone you are just making contact and introducing yourself)
The first time you visit the stone, scrub the stone with the holy water and brush to remove any work from the stone that might have been done by any practicing person at any point. I promise you're not the first practitioner to visit that graveyard in all the time it's existed. Once you've cleansed the stone, paid your respects to the spirit, introduced yourself, pulled any weeds, physically cleaned the stone of any garbage, etc it's time to get acquainted. Go around the area, have a chat using the cards to run a basic conversation for a bit. When it's time to depart for the day, promise the spirit of the headstone you will visit again soon and if you say what day you're going to visit make sure you visit on that day. You must treat it like a dinner date with a friend.
Exit the plot, pay 3 coins to exit where you first entered but on the oposite side of entrance. If done correctly on exiting you should feel the temperature return to the world. It should no longer feel devoid of energy or life. When exiting never look back EVER. Mist yourself with the holy water and the bottoms of your shoes before returning to your car.
The process of collecting graveyard dirt does take more than a day. It takes several visits of establishing trust and building a relationship with the spirit. It is a process and for what it's worth it isn't something that is gained quickly.
After a few visits ask the spirit if you can take some graveyard dirt from it's stone so that it can aid you in your spell work. If a yes answer is received then you may use that graveyard dirt as a powerful aid in any workings you may be doing to boost the work with the power of the spirit.
That said, it is very beneficial to use the gravestone of a deceased friend in life, a close family member or at a minimum someone that shares blood with you when possible. Typically these spirits already have your best interests in mind and heart. In addition you're running less of a risk when dealing with a familiar spirit.
Perform a banishing ritual upon returning home. Take a bath in hyssop and holy water.
Graveyard work is advanced. At a minimum if you don't have the skills to run your cards and pendulum, and know how to do the banishing rites properly wait until you do. It is a territory that can be very rewarding and you can get significant gains of power in doing so.
Gaining spirit allies is a very important step in advancing in your practice but don't mess around with it if you aren't prepared to deal with any unwanted outcomes.