With drip irrigation, irrigate for a predetermined amount of time, then go out with a soil probe and see if the soil is wet in the root zone, checking both the width and the depth. In sand, the water tends to go straight down. It's more difficult to use drip in sand. The water tends to spread out wider in clay. From my soils text book:
Texture, Available water per foot of soil
Coarse, .3 to 1.1"
Medium coarse 1.1 to 1.8"
Medium 2.0 to 2.9"
Medium fine 1.8 to 2.6"
Fine 1.2 to 2.0"
The "available water" would be at field capacity, which is how wet your soil would be immediately after a full irrigation. Therefore, if you soil is dry, you can expect to irrigate the amounts above to achieve field capacity.