Torque to appropriate load. Most seatpost require anywhere from 4 to 6 Nm, and they normally say what the Nm they require on the seatpost cuff.
If you don't have a torque wrench, and you have a bike with many carbon parts, I strongly suggest you invest in this tool. Frame manufacturers are not warrantying bikes that are cracked because of owners over tightening bolts. And one of the most common bolt that is over tightened is the seat post because people use the wrong grease. Horrible cycle.