Carving symbols to a candle is done to add properties, intentions, and representations. This can be done with different tools. I personally use a rose quartz tower about three inches in height. Toothpicks can be used for a softer wax such as paraffin, and harder tools such as needles, awls, stone towers, etc are better for beeswax, a much tougher wax to work than paraffin.
Petitions:
Petitions under a lot candle are also great for candle workings. These can get specific, act as taglocks, and include sigils and other symbols.
Taglocks:
Taglocks are personal items used to connect individuals to a working. I particularly enjoy using these with protection workings. To protect a family member I may use a button that came off their clothing or other personal items. As well taglocks can be used for many intentions. Buttons are placed atop a candle preferably as far from the wick and flame as possible. Be certain items used are not incredibly flammable and are placed properly and safely. Use caution. Smaller items are great.
Safety Tips:
When using candles magically never leave them unattended. Always use an appropriate holder for the candle type you are using. Avoid using plastic near your candle. Do not use plastic under your candle. Use a holder for the type of candle you are working with.
Dressing a candle for me is done with absolute care. Reverence is often felt during the process. Natural items for candle dressing are preferred. Oils are wonderful for scent and to add intent. Essential oils are a natural and wonderful choice. These can also condition your wax. Sometimes I will use fragrance oils for dressing. Homemade perfume may be able to be used as well. This is great for intent and a personal or signature scent. Base oils such as conola, olive or grapeseed oil can be used. Olive oil is an inexpensive option. Herbs can be added to your candle for another level of intent after your oil. These can be added to the top of your candle carefully. Keep these away from your wick and do not use plants which are toxic for burning.
Option for pillars:
An option for larger candles such as pillars, is to fill a fire safe bowl with water, and place the candle within this. This helps to keep wax from building up and spilling, and the wax can be read in a divinatory manner as well.
Wonderful post CrystalSeer, very informative. I would like to mention that if someone would like to add an extra dimension or layer to their spell work using candles then I would suggest learning how to dip or cast the candles yourselves.
This is what I do. I feel that by doing this it reinforces the intent behind what I am trying to accomplish because I am working my energy into the process. You can also add essential oils and certain herbs directly to the melted wax. Especially oils that you have rendered yourself, once again to add an additional dimension or layer.
You can find the supplies at any hobby or craft store as well as on-line relatively cheap. The internet is abound with instructions on how to actually dip or cast. Please, as CrystalSeer has pointed out taking safety precautions is very, very important. It might be counter to the magic you are trying to do if you burn your house down in the process.