1. Read the Prolegomena first, or at the same time. That book, which is both clear and SHORT, is Kants own account of what the Critique was meant to accomplish and what prompted him to write it. If you read the Prolegomena and think hes barking up the wrong tree, put off the Critique... until you change your mind. (The last bit doesnt apply to people taking a class, of course.)
2. Kants lecture notes on Logic can also be useful because they show how he believed philosophical thought should be organized and expressed. Regardless of whether you take his so-called logical method seriously, no one denies that *Kant took it very seriously*, and once you can recognize it in the Critique, many passages become much easier to follow.
3. Dont expect a profound spiritual or aesthetic experience. I value this book as the first really satisfying rational explanation of why the world makes sense (turns out it has to!), but I wont claim its any good as a guide to meditation, as a substitute Bible, as poetry, or even as prose. Contrary to his reputation, Kant is an excellent writer, but hes not trying to take you to a higher level here, or even to entertain you. At all. See also point 6, below.
4. Choose your text with care. Abridgments are tempting, but every sentence of the original is there for a reason. Make sure your translation includes the texts of both the first and second editions (Meiklejohn doesnt). Of the two translations Ive read, I can recommend Kemp Smiths often loose rendering (St. Martins Press) over the scrupulous but stilted Wood-Guyer (Cambridge), and both over either alone; but Ive heard good things about Pluhars Hackett translation too.
5. Dont skip the Introduction. Key points are made there, and key terms defined. The first time I tried to read the Critique I skipped to the first chapter of the main text (Transcendental Aesthetic) and it was like running headfirst into a brick wall. (It *is* all right to ignore the Prefaces on a first reading.)
6. Whichever parts you read, read every word. Its possible to skim through one of Kants arguments and get an accurate feeling for the meaning, but the details of the argument do matter, because he very often appeals to them later on – and also because, unlike so many other writers on the same subjects, he is trying to *prove*, not to cajole or enchant. Emphasis is important too, so you must read for context: does he mean *synthetic* unity of the manifold, synthetic *unity* of the manifold, or synthetic unity of the *manifold*? Its not that the concepts are different, but the author is pointing out something different about the concept depending on where and how he uses the phrase. Take the phrases, sentences, paragraphs out of context and they all sound like the same kind of hollow, pretentious, narrow-minded nonsense. I have found that the best way to preserve the logical connections is to READ ALOUD.
7. Question everything you read. Youll usually find that the statement was justified earlier (or, in some cases, will be explained in the next paragraph). Not only is this the safest way to read a book of Western philosophy, but it is the best way to *restore* the logical connections of the text once you have lost track of them, which will often happen.
Theres more I could say, but thats plenty to be going on with. Best of luck!