Sustainability in addition to the health benefits, dieticians say a plant-based diet is more sustainable, as it causes less harm to the environment than a meat-based diet.
Tips for getting started:
Here are some tips for switching to a vegetarian diet:

Start learning about the nutrients required, and how to obtain them.
Get some tips and recipes from vegetarian websites, a local health food shop, or a nutritionist.
Make a weekly shopping and meal plan.
Focus on a variety of meat-free dishes that provide complete protein, so that you do not end up eating as before, but just leaving out the meat.
Consider making the change gradually, for example, over a month.
Start with familiar meat-free foods, such as mac and cheese and salad, and add to your repertoire over time.

A gradual change may work better for two reasons:

It is more likely to become a lifestyle and a long-term move. Sudden dietary changes, such as an increase in the consumption of beans or vegetables, might lead to temporary digestive problems, such as bloating.
The Academy of Nutrition and Dietetics have a range of tips for people who want to stop eating meat:

Choose whole grain products, such as whole wheat bread, wild or brown rice, and whole grain cereals, as these can provide B vitamins.

Vary the diet, with whole grains, fruits, vegetables, legumes, nuts, and so on.
Use eggs and dairy products in moderation, or try adding soy milk.
Ask a healthcare professional about supplements, especially vitamin B-12.
Ensure a sufficient intake of vitamin D, especially if exposure to sunlight is low.
Check the labels of “healthful” vegetarian snacks to ensure they do not contain a lot of sugar, salt, or other additives.
Remember that junk food and fast food can be unhealthful and high in calories, whether they are vegetarian or not.
They also suggest reducing the intake of high sugar and high fat foods.

The nutrients you need:

Some scientists say that a vegetarian diet is beneficial to people of all ages, but they note the need to plan appropriately to obtain the whole range of essential nutrients.

The chart below lists some of nutrients that a person following a vegetarian diet may lack, how much of them an adult requires, and some examples of foods that contain them. Some people may also need supplements to boost their levels of these nutrients. Needs may increase during pregnancy and breastfeeding.
Nutrient Needs for adults aged 19 years and over Sources

Iron 8–18 milligrams (mg) Pulses, including beans, chickpeas, lentils tofu, spinach, cashew nuts, and green peas. Consume these with vitamin C, which helps the body absorb iron.
Calcium 1,000–1,200 mg

Yogurt, milk, cheese, tofu, fortified orange juice, kale, turnip greens, and broccoli. Calcium is essential for children and women around the time of menopause.
Protein 46–56 g

Eggs, milk, soy milk, nuts, nut butters, seeds, pulses, and cereals. Vegetable sources may not contain complete protein, so people should ensure they get enough of all types of protein throughout the day.
Vitamin D
15–20 micrograms (mcg)

Fortified dairy, soy milk, and breakfast cereals, alongside exposure to sunlight.
Vitamin B-12 2.4 mcg

Yeast, eggs, dairy products, fortified foods, such as breakfast cereals.
Zinc 8–11 mg

Dairy products, fortified cereals, dried beans, nuts, and soy products.
Iodine 150 mcg

Seaweed, yogurt, milk, cheese, enriched bread, enriched macaroni, prunes, lima beans, apple juice, green peas, and bananas.

A vegetarian diet will not guarantee good health, but it can contribute to overall healthful dietary choices. A person still needs to make healthful choices, such as avoiding added sugar and high fat processed foods.

Parents and caregivers of children who follow a vegetarian diet, should ensure the child is obtaining the nutrients they need for their age and stage of growth. This may include making sure the child is not just eating the family meal minus the meat.
What are the key nutrients a person needs?

The 2015–2020 Dietary Guidelines for Americans provide an eating pattern to help people eat healthfully on a vegetarian diet. It advises on suitable quantities of:

dark green vegetables
red and orange vegetables
starchy and other vegetables
whole and refined grains
dairy products
proteins foods, such as eggs, legumes, soy products, nuts, and seeds

People who follow a vegan diet may need supplements.

According to the Academy of Nutrition and Dietetics, a well-planned vegetarian or vegan diet can be healthful for people at all stages of life.

Plant-based diets may help reduce the risk of heart disease, cancer, type 2 diabetes, obesity, and other conditions. Plant-based foods also tend to be more environmentally sustainable than animal-based foods.

It is worth remembering, however, that going veggie will not make a person healthy overnight. To see improvements in health, it is essential to plan well, include a variety of ingredients, and make the diet part of an overall healthful lifestyle.

For people who wish to reduce their meat intake but feel this is too difficult, a gradual or partial switch may be a suitable option.

The American Heart Association (AHA) offer tips for going meatless, especially for people who would like to lower their cholesterol levels and decrease their risk of heart disease.