The First Burn

In order to maximize your burn time, you should make sure that the first time you light your candle you can do so for one hour per inch of candle diameter. For example, if your candle is 1.5 inches in diameter, you should let it burn for at least 1.5 hours. This is necessary to allow the wax of the candle to liquefy from edge to edge at the top. If you don't let the candle burn long enough to achieve this, you'll create a void in the center of the wax. This will cause the candle to “tunnel” and the flame will essentially dig itself a hole through the candle, wasting wax and limiting your candle's lifespan.

Wick Care

Most candles should not be left burning for more than three or four hours. This may vary based on the quality of the wick and the type of wax, but allowing the candle to burn for longer without cooling can cause issues.
As the flame of your candle burns, it releases carbon. This will collect on your candle's wick and cause it to split or “mushroom.” This will cause your flame to become too large, causing your wax to melt faster than intended and possibly be a fire risk. Burning this carbon will also cause your candle to give off a dark and unhealthy smoke as well.To avoid this, the candle should be extinguished and left to cool for at least two hours. This will allow the wax to re-solidify. At this point, you should trim the wick down to ensure that it is a single unbroken strand no more than 1/4 inch in length. Also, remove any loose debris from the candle and the wick itself.

Storage and Proper Cleaning

Your candles should be stored somewhere cool and dry, so your windowsill on a sunny day is not an ideal location. If your candle is in a container with a lid, ensure that you make use of the lid. This will keep your candle free of any dust or household debris. If not, give your candle a quick wipe with a dry cloth to clear away anything that may cause your candle to burn faster than intended.