Avoid window or open-air area. Crystal formed from water solution can be disappeared once contact with humid air
Too much water or not enough water will cause crystal growth to fail
Do not boil water in kettle or aluminium pan
Finish this step in 30 second.
Some tiny undissolved residue wont effect the outcome (in fact, it is the proof that your solution is supersaturated)
Make sure the temperature is cool down gradually. Wrap in towel to prevent a suddent drop in temperature
Make sure the arched surface is pointing upward
Using stirring stick and find the position of the growing based
DO NOT SHAKING OR MOVING THE VESSEL.
Keep the lid off the vessel so the water evaporates