I've been vegetarian for a bit over a decade (no fish, but dairy and eggs okay) - If you live in the right area, and have the right tastes, it's downright easy. In other areas, it's quite difficult.

My personal tips & notes:

* If you otherwise enjoy meat, there are a lot of meat-substitutes out there and more being developed. These tend to do a great job of mimicking processed meats and a terrible job of mimicking "real" meat. They also vary greatly. Quorn, Morningstar, and Boca (for example) all have very different tastes and textures, so if you don't like one try a different one. (I personally prefer Quorn for chicken-substitutes and Morningstar for beef-substitutes). OTOH, some vegetarians never had a big attachment to meat, and this is not an issue. (I am very jealous of these people).

* Eating out is by far the hardest. In areas with many vegetarians (say, Seattle), you tend to have multiple options, things tend to be clearly labeled, and waitstaff is used to getting questions. In other areas (say, Georgia), you have fewer options, no labels, and people act like you've accused them of something evil if you have questions. Either way, though, the majority of the menu becomes inaccessible to you.

* If you are trying to be mostly strict, be cautious when dealing with regional/cultural boundaries. While Indian food tends to follow the same vegetarian definition as I do (Jainian food is even more strict than I am), others don't (Chinese and Japanese tend to not consider fish or other seafood as animals, thus you'll find oyster sauce on the "vegetarian" menu, or dishes that have oyster sauce or some sort of animal-based broth that isn't called out as such (oyster sauce, fish sauce, pork, beef, or chicken broth, and/or shrimp paste in some curries). In the American South, pork isn't just a meat, it's also a seasoning. Most purely vegetable dishes (such as "green beans" or "corn") aren't vegetarian there :(

* How strict you want to be impacts how easy life is. Avoiding tangible animal-based meat = easy. Avoiding broths and lard = not as easy. Avoiding animal byproducts, such as most gelatin, use of bones in filtering, animal-based rennet in cheese , insect-based dyes and glaze = quite a bit more effort. Find a level you are comfortable with, because for most reasons, it is still far better to be a not-entirely strict vegetarian than a failed attempt at a strict vegetarian. I myself avoid gelatin and known insect products (no more Junior Mints :( ), and when cooking at home I get animal-friendly cheese and sugar, but when I'm out I don't worry about where they got their cheese, but will ask about broths and seafood-sauces.

* If you are a picky eater such as myself, be warned that many places decide to make vegetarian dishes more "exciting" by putting in every form of vegetable/grain they can think of. Like a supreme pizza, some people are glad for the variety, but most have something in there they don't like. (I myself can't stand green bell peppers, which is in, like, 90% of commonly available vegetarian fare :( )

* I first went vegetarian cold-turkey (ha!) in college...but after 6 months I stopped because I was seeing stars constantly. (It's actually pretty easy to get all your nutrients as a vegetarian, unless you're living on a diet of rice and mac&cheese like I was) I had, however, lost the taste for red meat (suddenly felt oily and flavorless), and noticed that certain salads I had disliked I now enjoyed. A few years later I tried again, but this time I did it slow. I dropped a category of meat each year, giving myself time to adjust my diet and make sure I had a variety of options. I believe I dropped beef (from the first stint), then pork, then poultry, then all forms of seafood. The next year I dropped leather products as an ethical choice, and I've been this way for over a decade without too much effort. Some extra food costs, a limited range of foods, and limited eating out options, but not so much that it's hard. Dieting, for example, is much harder.

* You will learn to hate the preachy, judgmental vegetarian-types that make life hard for us. Most vegetarians (in my experience) do what they do for reasons they consider good, and think it'd be great if others did the same, but feel no need to look down on others that don't, nor to inform them of their "evil ways". I mean, most of us ate meat for a long time and didn't switch the first time the thought occurred to us, so why judge others for being the same? Still though, people get very defensive and often assume you're one of the preachy types until you prove otherwise.

* ...You will also learn to hate how defensive people are in general. This is not restricted to vegetarianism. If you say you're on a diet, people will talk about how awesome their chocolate cake is. Mention you have diabetes, and they'll list the sugary foods they adore. Say you're vegetarian, and they'll talk about how animals just taste so good, or how happy they are to shoot Bambi. I've collected a few vegetarian jokes to help break the ice and show I'm not a jerk about it. (My favorite: 'Vegetarian' is actually based on an old (insert culture here - I tend to say 'Native American') word, meaning "lousy hunter")

* Oddly enough, holidays tend to be the EASIEST times. Everyone talks about the turkey, but a traditional big feast (at least in America) actually involves lots of non-meat dishes. I found this a good way to relax my family and friends - I provide a big meal that doesn't contain "weird stuff". Some of the more skeptical people still bring meat dishes, but even then they end up seeing that as a part of the whole, as opposed to be a contrast between "weird food" and "normal food".

If you decide to take the leap, I hope this helps!