To get the best burn out of your candle is first, purchase a good quality candle. We have found that cheap candles using sub standard ingredients (usually the ones made in China)are subject to not burning well. They usually have a terrible scent throw to boot. Sorry if this offends anyone but it often is the case.

When you burn a candle, especially container candles such as soy, a good rule of thumb is to allow the candle to burn long enough to create a complete pool of wax across the top of the candle. Each and every time you burn the candle you should allow this to occur. Wax kind of has a memory and the first time you burn it usually sets the tone for how the rest of the candle will burn. Many people make the mistake of only burning the candle a short period of time and it starts to tunnel down the middle of the candle. As a result, the walls of the candle become high and as the candle burns it eventually drowns it's self out because the pool of wax has no where to go. If you have a candle now where this has happened it might make it easier to trim the excess rim off by first lighting the candle, leave it lit for a while to soften the side walls of the rim. Blow it out and let the candle cool so no liquid wax can pour out, but not completely harden. This should leave the rim still soft enough to cut using a sharp knife. Be careful not to press too hard as to cave in the sides of the candle. Hope this helps.
Debbie