Japanese is remarkably difficult to learn, and more so as you get older. I'll go through some basics here, but if you're serious about learning the Japanese language, you should get yourself a good language course and study.
Just about any Japanese language course will be a great help, but naturally, some are better than others. I looked into getting associated with an online retailer to make a few pennies off referrals, but the terms and conditions for those programs are absurd. I'll give you a list of my favorite and not-so-favorite Japanese language learning resources. Feel free to pick from your favorite retailer, or ignore my advice and choose your own path. Different people learn differently, and what works for me may not work for you.
Use multiple sources: Using a single source for learning quickly becomes a hindrance. Decide on a structured language course, and then supplement it with some adjunct sources (more below).
All courses have their good and bad points: Mostly true. Most are good. Some are really bad. Different regions in Japan speak different dialects, and the courses sometimes reflect that. If you can, speak to other Japanese learners and get their input. Mine is below.
Find what works for you: Each of the courses below will teach you a particular vocabulary and sentence structure. Look them over, read through the first 3-6 lessons if you can (you remember libraries, right?), and decide what works best for you.
Avoid "easy" solutions: Anything that promises to make you fluent in a few hours of study most certainly won't. You know it. Don't fall for it.
Learn pronunciation from a native speaker. Learn the language from a non-native speaker: Native Japanese speakers are the definitive source for pronunciation, but they're not terribly good at explaining the language. Likewise, English speakers really aren't the best at teaching English. We tend to not think much about our native language, and why the language works in particular ways. People who have learned a second language have already figured out the quirks of the language and can explain them.
Living Language: Ultimate Japanese Beginner-Intermediate (Book and CD Set): When I first started learning Japanese, this is what I used. It's a conversation-based learning model, but it provides a surprisingly good introduction to the language. If you're going to Japan in six months to a year and want to learn enough Japanese to get around and chat with the locals a bit, this is a good choice. I'm not sure it's structured enough if you want to really learn the language.
Japanese for Busy People: This is a well known language course, and is probably my second favorite comprehensive course. It's also mostly conversation based, but it introduces language concepts in a structured manner and progresses through common conversations that you might actually use. Easy to understand and follow. I'm still evaluating this, but I'm happy with it so far.
Genki: This is another well-known language course. This would be my first choice as a resource for someone who really wants to learn the language. It introduces vocabulary and culture through dialogue, and teaches verbs in the dictionary format first. It provides a fairly comprehensive overview of vocabulary, grammar, culture, and writing systems.
Minna no Nihongo: "Japanese for Everyone" This course is unique in that it uses two books; one is exclusively in Japanese, and the second is the translation book for your native language. It's an interesting approach, and I've actually used this course, but it has some serious problems. Studying these books actually made my Japanese worse. My primary complaint (aside from requiring me to have two books open at all times) is the introduction of verbs. Instead of introducing you to the dictionary form of the verb (the infinitive form in English parlance), verbs are introduced initially in polite form, and later they give you a complicated method of translating back to dictionary form so you can then convert forward again to the other verb forms. Absurd and unnecessarily complicated. Do yourself a favor and avoid this.
Japanese from Zero: Don't. Just don't. If the (American) author can't speak English, do you really expect him to teach you Japanese? Just don't.
80/20 Japanese: An interesting e-book and web site from Richard Web. Again, I'm not sure this is sufficient as a complete course, but as an adjunct, I think this is excellent. He provides nice visual depictions of Japanese grammar that are extremely useful. If you're a serious Japanese learner, pick a comprehensive course, and then sign up for this four to six months in.
Japanese Step by Step: A book by Gene Nishi, this is a pretty mechanical description of how Japanese is spoken. As a reference, this book is excellent. Again, I don't think it's enough as a base language course, but it's worth picking up just as a reference.
Kanji & Kana: By Hadamitzky and Spahn. If you need to learn Kanji (and you do!) this is the book to get. Significantly better than the commonly recommended resources. Get the workbook and photocopy the pages for practice. If you're a serious student of Japanese, and working on learning the writing system, I can't recommend this enough. Best out there.
White Rabbit Press: White Rabbit produces Kanji flash cards that are very useful. The cards come in three sets, so start by buying the first set. When you know everything in that set, buy the second set. There's really no sense in buying all three sets at the same time until you know these are useful for you, and that you're actually going to get through them all.
Easy Japanese: By Jack Seward. When I bought this book, I hated it. The idea is to teach Japanese by learning pattern sentences and then you can just substitute words as necessary. In general, it's not a bad idea, and some other courses use this approach as well. My complaint with the book comes from the author's tone. He feels that if you can't understand Japanese with minimal instruction, you're just stupid. His disdain for everyone and everything is prominent throughout the book. Then, there's this sentence pattern from Chapter 3: "Dear me, grandma has fallen into the septic tank again!" No kidding. I'm fairly confident I'll never need to use that sentence. With all that said, I've grown to like this book quite a bit. Jack Seward may be an ass, but his insight into the Japanese language and how it developed into modern conversation is quite insightful. The sentence patterns, although often bizarre, are also more useful than the silly toddler dialogue that most courses use. If you can still find this in print, it may be worth picking up.
Pimsleur: Pimsleur offers a Japanese "course" that's (almost) completely auditory. Despite what they claim, this is not a comprehensive Japanese course, but it's very useful for hearing Japanese, and goes well with a real Japanese course. Download this (I mean, purchase the CDs) and listen to it while you drive, or while you fly to Japan. This is quite useful, even though it sometimes has some odd vocabulary and sentence structure.
Online resources: There's a huge pile of online resources for helping with your Japanese studies. Focus on the free stuff. Check out my Links for Japanese Learning section for some of my favorites. Search online for JLPT sample exams, and test your knowledge. Those sample tests are quite enlightening (or sometimes discouraging).