Reducing meat consumption or going fully vegetarian is easier said than done - here are a few handy tips from someone whose done it.
DO take your time with it. Even if you want to go fully vegetarian with all of your heart, don't rush yourself. If you've been eating meat all your life, it will be quite a change. You may find it easier to gradually reduce meat consumption until you reach the point where the task of shopping for a week's worth of meals sans meat doesn't feel like an impossible task.
DON'T be scared to try a bunch of 'fake meats'. This is by far the easiest way to replace meat as it still allows you to plan your meals as you normally would. Sausages, burgers, mince (you can even get mouldable mince now, for 'meatballs' and the like), hyper-realistic chicken... you name it, it's out there.
DO keep in mind that some 'fake meats' will be better than others. They used to be largely terrible just a few years back, and some still are, so DON'T let yourself be put off if you come across a stinker early on.
DON'T let people tell you that your diet will be lacking protein, vitamins and the like. Vegetarianism and veganism are different, so the easiest way to get protein as a vegetarian would be to gobble down a couple of eggs and a handful of nuts - but there is tonnes of protein in foods where you wouldn't expect it. You really don't need meat to get protein into your diet. Legumes are great too.
With that said, DO make sure you are getting all the nutrients you need. You can't just cut out meat and eat whatever would be left in your usual recipes - like mashed potatoes, condiments, and a salad sans sausages. If you start feeling more tired, for instance, it may be that you need more calories, iron, or protein. Keep an eye on what you're eating and make sure it's balanced, and DO consult a nutritionist if you are feeling different.
DON'T start preaching vegetarianism to everyone you meet. Unless they ask, and while you should be proud of your achievement, it does very little good to be lording your lifestyle choices over other people. If anything, you'll annoy them and make it less likely that they'll follow suit.
DO make exceptions if you have to. If you're just starting out, don't feel bad if you 'relapse' or make the odd exception while you're adapting to your new lifestyle.
DON'T be scared to try new things, and spending a little bit more time in the kitchen while you learn the ropes of a new diet. Some vegetarian food staples have disappointingly bad reputations - tofu, for instance, isn't bland and boring as some proclaim. They've just been served it wrong - smoked tofu is delicious just fried, 'natural' tofu does really well in a marinade.
DO remember that not everyone is comfortable cooking vegetarian cuisine. If you're invited to a friend's for dinner, there's no harm in asking if you'd make their life easier by bringing along e.g. a meat substitute of your own rather than having them venture into the daunting veggie aisle of the supermarket. Plus, this minimises the risk of them accidentally buying one of the aforementioned stinkers.
DO remember to celebrate World Food Day today.