Transfection is an essential cell biology technique by which one can introduce nucleic acids (DNA & RNA) into eukaryotic cells. It is particularly useful when one wants to express genetically engineered protein in cells (usually via plasmid DNA transfection) or deplete endogenous protein (via siRNA transfection).

The following is a list of what I think are the most useful tips for successful transfection, learned through years of experience and troubleshooting transfection experiments.