This is what I do, but there are many ways. I've developed my own style over the years. Flame/fire scrying is watching fire and letting yourself go. It can be interpreted through the physical behavior of the fire or your own intuition. I can't teach you how to use your own intuition. Just take note of any feelings, thoughts, or images you may see while gazing at the flame.
Before you start its always best to cleanse yourself. Cleanse yourself by either smudging yourself (native american tradition) or in any way you deam fit. Cleansing baths are good too.
Pick a room with no drafts! No air vents on! No fans! Keep the windows closed!
Check this by lighting incense. Watch the smoke. If its streaming up fluidly you're good to go. If its not, find a new spot or remedy the problem. You can also light a random candle (preferably the same kind that you will be using for the scrying) to make sure it burns normally and steadily. This also helps you to see what a normal flame from that type of candle looks like. Differently manufactured candles burn in various ways.
I use a virgin (brand new) short white tapered candle. I charge it with energy flowing from base to the wick and annoint it bottom to top with dragons blood oil all the way around (don't touch the wick with oil or it can start a fire. Stop the oil about an inch from the top). Roll the oil coated candle in crushed basil that you cleanse and charge for protective purposes.
I have a wrought iron candle holder that raises the candle and I place a large tibetain crystal point underneath it so that the tip is directly under the candle (you can lay it sideways with the base toward you, and the point facing away from you).
You can use quartz but I like my 3in tibetian crystal as it was a birthday gift from a dear friend. Any candle holder will do. If it has a wide base you can lift the candleholder up with clay, little blocks of wood, or flat rough stones. Keep it natural materials and anything will do. If you can't prop it up, just make sure that the point of the crystal touches the holder and the base is facing you.
Then I place sea salt in a circle around the candle.
If its for someone else I take a smaller quartz crystal point and place it on top of a piece of paper with the person's full name, birth date and address. This sits in front of the candle so that the candle is closest to me. The quartz crystal point faces toward the candle on the outside of the sea salt circle. Then the larger crystal underneath is turned around so that the base faces the paper.
Before you light the candle guide your energy to naturally flow into the salt circle, through the base of the crystal and up through the tip into the candle, ending at the wick. If it is for someone else, see energy from the person (paper) flow from crystal to crystal and up the candle. When you feel this connection is secure....
Ready? Light the candle with a match (no lighters!)
This process does two things. It protects the candle from unwanted influence and gives you full control. It also puts you in the right mindframe and gives you a direct uneffectable link.
Sit in front of the candle and gaze (don't stare) at the flame.
This can take up to 10min to see results.
If the flame is small and bright there is no magick maliciously effecting you.
If the flame looks darker than usual, won't stop flickering, or it continually "fights" to stay alive (getting low then high then low) you have a harmful spell on you.
If the flame splits off but looks good (even if the split off is dark) it means that you have an enemy (a threat). This could mean a malicious spirit or a physical person with the desire to harm you. The more splits, the more enemies. I've once seen a candle flame split into 5 seperate flames.
If you scry and you get confused over what you're seeing, write down your observations and feel free to pm them to me. I can help you sort them out. But its best that you let your intuition decide for you right then and there. Trust your instincts.
REMEMBER this is not your power moving the flame. This is allowing the element of fire to guide you and using your intuition to pick up signs. Your mind will pick up what it needs to see in order to give you the proper information.
This can go straight into a SPELL BREAKING ritual. I replace the candleholder and tibetian crystal with a cauldron (or bowl that is to never be used for cooking). I take the same candle and mount it into the bottom of a bowl (you can use a small glass/crystal holder, I use clay). And slowly fill the bowl with blessed water about an inch or two from the flame. Concentrate on the flame and that the flame is the spell. Watch as it extinguishes itself in the water. Pay attention to the floating basil in the water as the candle burns within, scry a little with it. It can be used to show you the goal of the spell and even hints to who it was.
Never touch the water! Once the spell is extinguished take it outside dump it into a hole in the ground, a sewer or dump it into the toilet. Once half the water is out, you can use a black cloth to remove the candle, then continue pouring the rest of the water out.
Wrap the candle in the black cloth and bury it as soon as possible as far away from your home as possible.
Its best to cleanse and protect yourself after you have uncrossed yourself.