Health is a constant process of re-evaluation and improvement.
For many, making the change to vegetarian (or vegan, even better) lifestyles can be a huge shock, which can make it unsustainable despite best intentions.
Here are some tips on getting started:
1) One a Day
start by making one meal a day vegetarian or vegan.
I think breakfast is a good starting place since there are many breakfast foods that are easily available and that already fit the bill. Go for oatmeal, bran flakes (not frosted flakes), granola/muesli with soy milk, whole wheat toast with natural jam and fresh fruits. Make yourself a healthy smoothie or fruit shake, or some fresh-squeezed juice to wash it down. Since this is the first meal of the day, you can have your carbs now.
When you can do this for a month or more easily, you can move on to two meals a day.
2) Red = dead
In the transition phase, if you must continue to eat some meat, keep to "clean meats" such as chicken or fish/seafood. Avoid fatty meats and red meats, whose proteins are the worst for you. Watch your protion sizes and remember that most of this craving is mental and can be overcome. Keep your ultimate goal in mind and don't be too hard on yourself. Stay the course.
There are many things you can put into foods to replace meat. One of my favorites is shiitake mushrooms, which I slice up to replace slices of beef, or finely chop to replace ground beef. With some tomato paste, mushrooms are a big hit of umami, and their savory flavor can give your body the same satisfaction without ill benefits. Tofu isanother mainstay. For those who cannot do without, TVP (textured vegetable protein), TSP (textured soy protein), and Seitan are all good vegan substitutes.
There are vegan versions of many popular meaty dishes/condiments such as mayonnaise, butter, shortening, chili, bouillion, burgers (some of these are FANTASTIC!), lasagna, burritos, chicken nuggets, etcetera.
4) Snack Time
A lot of vegetarians/vegans blow it here. Plan ahead, and surround yourself with healthy options such as nuts/dried fruits, veggie sticks w/dips, healthy chips (minimal salt, baked not fried), healthy energy bars (some fantastic ones are available!). Humans like the convenience of grazing, and so we grab what is nearby. Think about what is in reach during snack time. High sodium notwithstanding, I am a big man of instant miso soup for snacktime, and of miso in general.
5) Water Bottle
I keep a one-liter water bottle on my desk and have a full one in the morning and a full one in the afternoon. I also drink water with most meals, so that gets me to between 3-4 liters daily, which is what I want. Stay away from the coke machine.
I also kept a variety of good healthy herbal teas in my desk for when I wanted something else.
6) Turning Japanese
Japanese food is some of the healthiest on earth (and Japanese live very long lives because of it). I am usually happy and satisfied after a bowl of rice w/nori topping, miso soup, and some tofu. There are healthy rice balls, and a variety of Japanese side dishes that are completely vegan and taste AMAZING! These are also usually very easy to prepare, so a Japanese diet is a great way to get healthy. My Japanese wife constantly amazes me by the traditional Japanese vegan foods she serves me.
Even if you picked only one of the points above, it would be a good start.
Try it for a montha dn see how you feel. Notice that you sleep better, have more energy, and feel better about yourself. This stuff can change your life.