Many plants require about an inch of water a week. An easy way track rainfall is to place an empty tuna can somewhere in the garden. When the can—which is approximately 1 inch high—is empty, it's time to get out the hose. Another way is to just stick your finger an inch deep in the soil and judge the moisture there. You aren't afraid of getting some dirt under your fingernails, are you?
Once you get a sense of how much water each of your plants needs, consider making up a weekly, biweekly or monthly schedule to make sure you don't over- or under-water.
So much beauty in dirt