Are you asking about common errors people make when using a reflux condenser? If so:
1) Make sure to stir your solution or add boiling chips to your solution before heating. Failure to do so can cause your solution to superheat and cause bumping.
2) Don't fill your flask more than half-way when boiling solutions. Boiling solutions produce hot gasses. Hot gasses expand. Expanding gasses in enclosed spaces can cause explosions.
3) Remember to cool your reflux condenser. If it is jacketed, water should go in the bottom connection and out the top connection. If it is not jacketed, wrap a wet paper towel around the condenser to keep it cool.
Hope this helps.