The main problems with hand dipped tapers are blisters and lumps on the surfaces of the candles, a ripple effect on the sides, or candles that are skew. These are problems I have encountered using fully-refined paraffin wax, with no additives. I haven't made tapers using other types of waxes yet.

Blister-like bubbles or lumps: the dipping wax is too cold. Dip your tapers at 71°C (160°f). If you use a temperature-controlled pot, that's great! It will save you lots of time and trouble. If you use the ordinary stove-top set-up, you will just have to monitor the temperature very carefully in between dipping.

The ripple effect: usually this means that you haven’t left enough time between dipping each layer. Leave at least 1 minute between dippings. If you work in very warm weather conditions, e.g. 30°C (86°f) or above, wait for two minutes before you dip the next layer.

Skew, bent tapers: make sure your dipping pot is longer than your candle, so that the candle doesn’t bump against the bottom. Give the wick an initial dip of 1 minute before you start dipping. Straighten the wick between your fingers and hang up for one minute. Before each dip, hold the candle by the wick and the bottom end and gently straighten.

It takes practise, but your hand dipped candles will improve, if you apply these few simple remedies.