1. Don't print unless you absolutely need to. This includes emails, receipts, invoices, tickets, etc...
2. Try to use electronic visiting cards
3. Try to avoid printing wedding cards
4. Avoid printing draft copies of anything. Most of the time, the computer will give you a very accurate representation of reality
5. Re-use. Use the back sides of single-size used paper for rough-work or printing if possible
6. There is sufficient debate about paper v/s plastic cups. Please do let me know if a consensus is reached either way

1. Most tanks these days have a half-flush option for the not-so-intensive flushes. Use it if and where applicable. Kudos to the one who came up with this!
2. Another trick to save water in tanks is to keep a full 1 litre bottle of water in the flush tank so that it always fills up 1 litre of water less and you will save 1 litre of water on every flush. Considering an average of 6 flushes/day, you will save about 2190 litre of water every year!
3. Avoid leaving the tap on while brushing, shaving, lathering your hands, etc...
4. Try to use a soap that saves water. This includes bathing and washing clothes
5. Try to use a front-loading washing machine. They are not only more power-efficient but also need lesser water as compared to top-loading ones [1]
6. Be generally aware of how much water you use and try to cut-back if and where possible

This may be slightly questionable in its classification as a natural resource, but since most of the electricity in the world today is produced using natural resources [2], I am including it here.

1. Turn off your mobile/laptop/any-other-device-charger when the device is either fully charged or is not plugged in for charging. Your charger will consume electricity even if no device is pluggin-in to be charged. This is because most chargers use a step-down transformer which works on the principle of induction [3]
2. Turn off all lights and fans when not needed (this goes even without saying) and includes your home, office and school
3. Try to avoid using hot water in the washing machine. About 80% of the washing machine's rated power consumption is due to heating of water.
4. Try to use a front-loading washing machine. They are not only more power-efficient but also need lesser water as compared to top-loading ones [1]
5. Try using LCD/LED monitors as opposed to CRT monitors
6. In large software establishments (such as data centers), use runtimes that use less power or don't use a runtime at all. i.e. Avoid Java, use C++
7. Try to turn off your monitors when they are not being used
8. Try to keep a screen-saver that will turn off your monitor as opposed to showing cute animations
9. Try to use appliances that are energy-efficient. Ask your dealer about this since it would vary from region to region

Note: Just using lesser electricity won't solve the problem. The reason being that power generation companies will still produce as much power as they did earlier in anticipation of all being used. However, over time, they will see the reduced usage (based on bill payments and other means) and will accordingly adjust the amount of electricity generated.

Remember: Your contribution - however small - WILL make a big difference in the larger scheme of things.