The natural stickiness of beeswax makes easy candle removal impossible. Up to 10% beeswax added to paraffin wax, and you can still get the candle out of a 2-sided plastic mould. Any higher percentage of beeswax, and you'll have to lubricate the moulds, to get good candle separation.
For metal moulds, use a candle release spray or lotion. These lubricating sprays are available with or without silicone.
For plastic and acrylic moulds, don't spray with silicone, it corrodes the mould. Use mold release alternatives suitable for plastic moulds instead.
Use vegetable cooking oil as a substitute. This natural release agent works equally well in steel, or plastic moulds. Rub a thin layer onto the inside of the mould with a soft, lint-free cloth, (to avoid scratches). Stand the mould upside down on newspaper. Allow the excess oil to drip away. Give it a final rub, and pour your candle.
I've only worked with paraffin and bees waxes, and cannot give you tips for other wax types.
How to Separate a Stuck Candle from its Mould
Now I can hear you say, "Yes, but that doesn't help me at all, the candle is ALREADY stuck, how do I get it out?"
Run boiling water over the outside of a metal mould for a few seconds, and pull hard on the candle's wick. The candle should slide out fairly easily. If you're very fortunate, the candle will be undamaged, (but that's unlikely).
With a completely stuck candle, that won't budge, you'll have to put the mould, candle and all, into a metal dish with boiling water, and melt the candle out. Remove the soft candle after a few minutes. This candle mass can be dried off and melted down at a later stage. At least you won't lose all of the wax.
Leave the wax residue in the water to cool down. Lift this wax layer off the water, and dispose of it in the bin. Never
throw melted-wax-and-hot-water down the kitchen sink, or drain.
For plastic and acrylic molds, follow the same procedure, but with hot, not boiling water. Pour hot water over the mould, and pull the warm, soft candle, from the mould. Some plastic moulds are heat-resistant up to 110°C (230°F), but some start warping above 82°C (179.6°F).
Consult the instructions that came with your moulds, to check up on the correct temperatures.