1. Keep it simple, go slowly, and don't strain. Cut back on red meat first, then gradually eliminate it, then start the same process with chicken and fish. At the same time, gradually introduce new vegetarian foods to your diet.
2. Go organic as much as you can. Organic food may cost more, but it's generally tastier and more nutritious (that varies with the quality of soil used for growing).
3. Get yourself a basic vegetarian cookbook, to start with
4. Avoid sugar and junk food, including soft drinks. Be sure to eat a well-balanced, widely varied, nutritious diet, to get all the essential vitamins and minerals.
5. Drink mostly water and other clear fluids. It'll help the inevitable de-toxing. Plus, there's more bulk, or roughage in a vegetarian diet, and you need plenty of liquid to keep it all moving through your digestive system.
6. Listen to your body. It isn't normal to feel tired, weak or ill on a vegetarian diet. Get regular checkups, and go to a doctor or nutritionist if you're not feeling well.
7. Stay away from extreme diets
8. Don't worry. Vegetarian food takes some time to get used to. You may not feel quite full enough, at first. Follow this general guideline: eat three meals a day, chew your food well to help your digestion process all that fiber, be sure to have protein from several different sources every day, try a variety of whole grains and fresh vegetables.
9. Enjoy your food! If you don't like something, or it doesn't seem to like you, you don't have to eat it! There's such a variety of food available for vegetarians, enough to satisfy everybody's tastes and nutritional needs.
Source: Savvy Vegetarian