Make master mixes whenever possible to reduce measurement error, especially when working with small volumes. Add extra 2-4% to be sure you got enough for all your samples.
Enzymes in 50% glycerol: Do not submerge the pipette tip deep as too much enzyme will be aspirated due to glycerol's viscosity
Viscous liquids (e.g., glycerol, mineral oil):
Pre-wet the tip by pipetting up and down before taking the final amount
Can also fully press it to aspirate, then release to the soft press, and discard the rest
Volatile liquids (e.g., ethanol): Hold the pipette at an angle after aspiring the final amount and work fast as the liquid quickly starts to drip.
Always watch that all components enter and exit the pipette tip.
Balance your tubes roughly by volume. It need not be perfect: for instance, when balancing spin columns, people often use a different kind of a column as a counterweight (if the correct one is not available, of course).
For larger centrifuges, balancing is done by weight of the entire thing that you put in the centrifuge, including, for instance, a paper label.
Do not overfill your tube in such a way that once it is tilted in the centrifuge and there was no cap, the liquid would spill.
Keep your reagents on ice unless specifically mentioned otherwise.
Aluminum and water-based Eppendorf racks warm up at about 3-4 deg/min. Thus, if you take something from -20C, in about half an hour your sample will reach 0 deg and in an hour it will be room temperature.
Dilutions: Final conc. = Stock conc. x Input vol. / Final vol.
Concentration in M = Mass (g) / (Molar weight (g/mol) x Volume (L))
1 uM = 1 pmol/mL
DNA weight to concentration:
Concentration in nM = 1623 x Concentration in ng/uL / Size in bp
When preparing solutions, first dilute components in a smaller amount of a solvent than the final amount would require, then add to reach the final volume. This is done because the volume may change when solid components dissolve.