It depends on the type of vegetarian diet you are trying to adopt.
One of my kids is vegetarian and won't eat "anything that had a face", but will have dairy products and eggs. Some people choose a partial vegetarian diet - chicken and/or fish is ok but anything with four legs is not. Other people are vegan and won't eat or use anything that comes from an animal (no bristle brushes, no leather shoes, no honey, etc).
Lower calorie intake can make you light headed. So can spacing out your meals too much. You may find that you need to have more frequent meals to keep your blood sugar level on an even keel.
I try to make sure that vegetarian meals are well balanced, ensuring that the dish includes a legume (chick peas, lentils, beans) and a grain/starch (rice, pasta, potatoes) in order to provide a complete protein. The other day I made a vegetarian curry with chick peas, cauliflower, onions, tomatoes, celery, carrots, beans and peas, which was served over basmati rice. It was so delicious - Mr Scully didn't notice that it didn't include any meat.
Check out some vegetarian recipes online - there are lots available.