how to use sleep function to save power

I'm wanting to have a remote arduino take daily readings at a stream using the vernier interface shield. Since it doesn't need to be taking data more than once a day, I'd like to reduce power consumption. Is it possible to use a sleep function in some kind of way to do this? These are very remote sites where data would be logged onto an SD and would only be checked monthly. I could try a higher amp-hour battery with charge controller, but was hoping that i could learn ways to reduce power consumption in the program itself if possible.

Nick Gammon has a nice overview of various levels of sleep
Gammon Forum : Electronics : Microprocessors : Power saving techniques for microprocessors.

using the vernier interface shield

One general GotYa' with sleeping the Arduino, is that it doesn't normally reduce the current taken by any shields you are using.

If the shield takes a lot less then 1mA, it will flatten most small batteries in a week.

You need to consider strategies to turn off the power to the shield e.g. fit a P Channel Fet in series with the supply and get the Arduino to turn the FET on when you need to use the shield

You need to consider strategies to turn off the power to the shield e.g. fit a P Channel Fet in series with the supply and get the Arduino to turn the FET on when you need to use the shield

Well, at least I know what a FET is, even though I've hardly used them! LOL Is there a tutorial of some kind that covers this?