Rule #1 - Starting with healthy plants is critical. Many of us don't live in a area with specialty nurseries. Don't fret. You can get excellent results by ordering your plants over the internet. Here is an important hint: Go to Google, enter the Nursery Name, add "+ review" to your search phrase. No reviews? Check the warranty. I have not had very good luck buying plants from discount stores and warehouse stores.
Rule #2 - Learn your USDA Zone Number and select plants that will grow in your zone. Be sure to consider your high and low temperatures.
Rule #3 - Where you place the plants is critical. Be sure to put them in the right place in your yard--sun-loving plants in the sun, shade-loving plants in the shade. Obvious, but important.
Rule #4 - You will want to provide your plants with complete nutrition. Plants of all types love humus. Manures (if sterilized) are excellent sources. My favorite is worm castings I make recycling my garbage.
Rule #5 - Most of us don't water your plants properly. The thirst stress can set back or even kill your plants.
Rule #6 - Don't let pests take over your garden. Keep an eagle-eye on the plants on the look out for signs of insect damage. There are safe (organic) ways to protect your plants and you at the same time.
Rule #8 - Apply mulch generously around the plants, but don't bury them. It is easy to pull weeds growing in mulch, which they will, than from the soil. At the end of the season, apply 2 or 3 inches of quality mulch.
Rule #9 - If you are plagued by deer, rabbits, squirrels and other animals. They may try to feast on your plants. If you see evidence of munching, use humane animal repellents. Some gardeners have had success with moth balls. Deer hate Repel.
Rule #10 - I know when you are in the garden working away. It is great therapy and fun to boot. Still, protect yourself. Wear a hat and gloves. Use sunscreen and watch for stinging insects. Use safe products--many common gardening products are not organic or all natural.
Bonus Rule- Have your soil tested. You might be surprised at what is missing.