1. Take an aliquot of chemically competent bacteria from the --80C freezer and thaw on ice. Bacteria must be kept cold at all times until the heat shock, or they will lose competency. Do not leave bacteria thawing for longer that 15 minutes. The bacteria should be good to go after 7 minutes.
2. Add diluted plasmid DNA stock (1-10 ng, e.g. dilute 1 uL of 1 ug/uL plasmid stock into 1 mL of water, and add 1 uL to bacteria) or 10 uL ligation reaction MAX to 50 uL bacteria (~5 uL is fine to be safe). Be sure that the volume of DNA solution added to the bacteria doesn’t exceed 20% of the bacterial volume (20 uL for 100 uL bacteria, 10 for 50, etc).
...