Strip a liquid class down and what is left is a translation: it takes the physical behavior of a liquid and turns it into numbers an instrument can follow. Once you know which properties matter and which way each one pushes, tuning stops being guesswork. Here are the properties that shape almost every class, and the parameter each one tends to move.
Viscosity
Viscosity is resistance to flow. Water is thin, glycerol and honey are thick, and the range between them is enormous. A viscous liquid cannot keep up with a fast plunger, so it needs a lower flow rate and longer settling times, and it favors a surface dispense over a jet. Get this wrong and you aspirate air or short-fill.
Density
Density is mass per unit volume, and it is the bridge between weight and volume. You need it to turn a gravimetric measurement into a delivered volume, so it underpins validation. Density also warns you about suspensions: components of different density separate, so a class for a settling mixture may need a mix step or a quick aspiration before it separates.
Adhesion and cohesion
Adhesion is how strongly a liquid sticks to other surfaces, such as the tip; cohesion is how strongly it sticks to itself. A highly adhesive liquid resists leaving the tip, so it needs more blowout. A highly cohesive liquid holds together, so it needs less air behind it to stay put, though it may still want extra blowout to detach. Chemical compatibility rides along here too, since some liquids attack tips or labware.
Capillary action
Capillary action is a liquid climbing a tip against gravity when adhesion beats cohesion. It is easy to ignore until you work at 10 or 50 microliter scale, where it can pull in more than you intended. At small volumes, watch for over-aspiration caused by a liquid that wicks up the tip on its own.
Surface tension
Surface tension is a liquid pull toward the smallest possible surface. High surface tension liquids stay in the tip and do not need a large air buffer, but they cling to the source, so a faster swap speed helps break the connection as the tip leaves. Low surface tension liquids leave more readily and may need more air behind them and a shorter settling time to avoid drips.
Contact angle
The contact angle is the angle a droplet makes with a surface, and it tells you how a liquid wets labware. A low angle spreads thin and makes low volumes hard to pick up; a high angle beads up and can be repellent. On difficult surfaces a bottom touch or side touch helps place small volumes reliably.
Vapor pressure
Vapor pressure is how eagerly a liquid evaporates. High vapor pressure liquids, the volatile alcohols and ethers, drip and off-gas, so they call for anti-droplet control, a larger blowout to leave room for vapor, and often a pre-wet of the tip so the first transfer is not the odd one out.