There are a couple of strategies that you can use. But before i get into that let me tell you that it totally gets easier with time.
Next thing, and i know that this is going to sound a bit crazy. But animal products are addicting. physically. I've included a couple of sources so that you don't think i'm a crackpot.
Also some non vegetarian food is sort of "comfort food". reminding us of happier times or whatever. I know a vegetarian girl who after her mother died has a strong craving for roast beef - well it turns out all thru her formative years, her mom cooked roast beef every Sunday.
and finally, and i want to stress this: Cravings are rarely based on any real need or deficiency. The pregnant lady who has to have pickles and ice cream is a great example. Most of the time, cravings are just mental hiccups. glitches in our brain.
Ok, this isn't necessarily a strategy but it should help. Almost all the experts agree that it takes just 3 weeks to break a bad habit or to create a new one. So if you could just make yourself go three weeks in a row as a good vegetarian - the habit will be ingrained. you won't have to think about it - it will be effortless. That kind of payoff at the end of three weeks should be enough motivation to power thru.
Also by the end of three weeks, you should be thu all of the withdrawn problems.
Ok, now for the strategies. Be aware of what is triggering the temptations. Try to avoid them. this is one of the few times avoidance is a good strategy. but just being aware of them really helps a lot. For instance you go into a restaurant and you smell roast beef and suddenly you think you want roast beef. You can just say to yourself. No. I don't want roast beef.
Kind of dove tailing with the above strategy is substituting. I used to make sandwiches, just like I used to before i was a vegetarian - just not with meat. I would toast the bread, put on the mayo, mustard, lettuce, tomato, (cheese?). You can do that with a lot of meals. Chicken fetucinni without chicken. BLT without B. Beef stew without beef.
When you do give in to temptation, think of it as a learning experience. why did it happen? what can i do to prevent if from happening again. What can i do to make resisting temptation easier? this type of behavior is much better than feeling guilty.