The first thing you need to focus on are your staples; pasta, brown rice and other grains, you will need these not only for protein and energy, but also to fill you up, because from my experience, vegetarian meals don't fill you up like ones with meat (which I think is good because i always felt too full after eating meat, but you also might feel hungry sooner after you eat)
Then you need to figure out where your going to get the rest of your protein from, nuts, seeds, beans and peas have lots of protein as does peanut butter, hummus, spinach and broccoli
Remember to eat lots of fresh fruits and veggies either with your meals or as a snack
If you think you will be craving meat during this transition, go to the grocery store and check out some of the 'fake meats'
you can pretty much find anything from hotdogs and burgers, to lunch meat and chicken patties. Most of these are delicious and do a very good job at imitating meat. Just remember, you shouldn't eat these all of the time, because they are processed, just like you shouldn't eat real hot dogs everyday. But they help a lot with cravings.
Also, make a list of your favorite foods and figure out how to make them vegetarian, for example, I loved mexican food like fajitas, burritos etc, so instead of putting meat in them, i put rice and beans in them. This helps because you can still eat your favorite foods, you just have to tweak them a little bit
Try looking up some vegetarian recipes online or get a vegetarian cook book for more meal ideas, just google vegetarian recipes, or go to recipezaar.com where you can look up recipes by ingredient.