Do you know what you're going to eat tomorrow? Can you make a meal plan that you'll stick to for a week (or a month) right now?
If you can't from the top of your head, think about the time you need to find a recipe and cook (maybe that's super easy because you know how to cook and you have an awesome cookbook!). If you need lots of time, being vegetarian first isn't a bad step. Lots of common meals are vegetarian (like mac n cheese) and makes it easier to start.
If your goal is becoming vegan, starting with a small step is not so bad. If you need to do a lot of research to become vegetarian, going vegan right away might not be the best approach.
If you already know what you think you need to know, and just need to start doing it... Go for it!
Be compassionate with yourself if you fail to live up to your goals. You don't need to be perfect today, the idea is to create a habit you won't break.
Pro: Might make it easier to stick to in the long run
Pro: being vegetarian for a while gives you a sense of accomplishment
Pro: Gives you time to get used to "being different" (if this is an issue in your social circle)
Pro: Lots of time to research vegan food while you enjoy a more cruelty-free life style than the one you had before
Pro: Easier to get into if you're unused to a vegan/vegetarian lifestyle
Con: Maybe you think "this was hard enough, how will being vegan feel like?" and give up on it.
Con: Your goal is being vegan, so you might feel bad about not being vegan yet.