If you don't have a gauge on your mini pump, the solution is simple: Pump until your elbow feels like it's about to either explode or snap right off your arm. When you reach this point, you'll have about half the air you need.

Translation: You'll know when there's enough air to support your weight. Your main concern, as others have said, is to pump enough air into the tube so that it doesn't "fold" into the edge of the tire and get snipped off between the tire bead (the inside edge of the tire) and the rim.