Making the change from being a meatie to being a veggie can be a daunting prospect. The first step if you're now in that position is to decide how you're going to make the change and when. Some people set a date for themselves while others say that they'll start their new diet the next day. Other's just say 'from now'. There are pro's and con's to all ways of doing it.
Giving yourself chance to prepare is good but then you know when you sit down for a burger the day before you become veggie that it will be your last. Starting the next day or starting straight away doesn't give you any preparation time but at least you don't sit and agonise over your last meal as a meatie. It's up to you. It's also up to you whether you give up everything at once or in stages. The 'stages' approach might mean cutting out meat first, then fish and then slaughterhouse by-products or starting with one veggie day a week and gradually working towards being veggie.
Having made the change you MUST if you haven't already, let everybody know, especially your parents. Not only will it make them more likely to accept your choice if you give them a bit of warning before they make you a meatie meal, it will stop you being tempted to re-adopt your old habits. You are more likely to become a meatie again as a new veggie than as an experienced one so get yourself some support. The links section of this website will get you started. Also, contact the Vegetarian Society (VegSoc). VegSoc is the authority on vegetarianism in the UK and they're a great bunch of people who'll give you loads of support. The VegSoc youth team is fantastic too and I recommend you join the Society as soon as you're fully veggie.
A balanced veggie diet includes fruit and vegetables, grains, nuts and seeds, beans and pulses and meat alternatives as well as veggie versions of non-veggie sweets in moderation. As I know too little about nutrition to give you any guidelines on obtaining specific things, I can only recommend sources of info. for you.
Viva! (Vegetarians International Voice for Animals) produces (amongst other things) two brilliant resources which will get you started- a magazine called 'It's Time to go Veggie!' and the short but invaluable guide 'The L-Plate Vegetarian'. Viva! founder Juliet Gellatley has also written a book for teenagers called 'The Livewire Guide to Going, Being and Staying Veggie'. It's been a real help to me and you can find it in all good bookshops.
Things to avoid include gelatine (boiled bones and tendons), suet (a type of animal fat), E120 (a red insect-derived food colouring wich is also called cochineal), carmine (a pink food colouring made from cochineal) and rennet (an enzyme from the stomach lining of calves). You will find a more comprehensive list in the resources listed above and in my Games section.
Staying veggie gets easier as time passes for several reasons. Firstly, you get less aggravation from your parents and friends as they get used to your new diet, see that you are still perfectly healthy and get bored of making fun of you. Secondly, you find more and more alternatives to meatie foods you liked and discover delicious foods you'd never tried before. Thirdly, you find out so much about the cruelty to animals in the meat industry, the diseases meat causes and the environmental impact of a meatie diet that you can't stomach meat again and finally, you lose the taste for meat along with, in some cases, the ability to eat it without being sick.
Until you finally lose those meatie cravings, you have to rely on willpower. Many of the hard-hitting leaflets distributed by Viva! and Animal Aid will banish cravings immediately as will many of the websites in my Links section. If all else fails and you do eat something you shouldn't, don't beat yourself up too badly. The same goes for if you eat something thinking it's veggie and then find it's not. Accidents will happen and you can't feel too guilty when they do.