Before we begin, I want to give you some notion of what lies ahead. Learning a foreign language - and this is perhaps more true of learning Japanese if you are from an English-speaking background - is unlike learning anything else. It uses a completely different part of your brain from Chemistry or Water skiing.
When I'm about to learn something new, I've always found it helpful to get a big-picture overview at the beginning. This helps me come to grips with the scope and structure of the thing, so at any point during the learning process, I know where I am, where I've been, and where I've still got to go. That's tricky to do with a language, but here goes:
Grammar
That sounds silly, but think about it - if we are going to talk about verbs and adjectives and adverbs... you'd better know what they are, and how they work in your own language. Otherwise, you won't be able to make a mental map to navigate your way around Japanese grammar.
For example, if you want to be able to say, "Please come to the office early tomorrow" in Japanese, you need to know whether "early" is an adjective or an adverb in this sentence. In Japanese (and, I assume in many other languages) the adjective "early" and the adverb "early" are different words. But that's no problem at all if you know your way around English grammar.
So if your English grammar is a bit rusty, there are several sites on the Internet that can give you a quick refresher.
That said, there are many dark corners of English grammar which will not help you at all in Japanese (or, probably, any other language). Just the basics will be enough.
Japanese, naturally, has a lot of its own special grammar too, with no equivalents in English. You will learn those along the way. Not speaking from personal experience, but still with some confidence, I can tell you that learning Japanese is not very similar to learning French or German. English came in part from those languages, and developed alongside them in Western Europe. Japanese developed in varying degrees of isolation in the Far East, alongside a whole lot of other languages which would be just as foreign to English speakers.
Japanese is very different to English, but that doesn't necessarily make it difficult - as long as you know this up front.
I will demonstrate that Japanese grammar is like a computer programming language. Very logical, ordered, efficient, with rock-solid rules that almost never let you down.
Vocabulary
Another consequence of English growing up with the other Western European languages is that a huge number of their words look like our words. Japanese words of course look nothing like our words... or do they? Actually, modern Japanese - especially that spoken in business - contains a huge amount of words borrowed from English. Often their meanings have changed after entering Japanese, but they haven't been in Japanese for long, so the etymology is usually easy to guess.
Japanese has a lot of words. Many times more than English. Or, at least that's what it seems from the number of entries in dictionaries. The truth is that many Japanese words are made up of little pieces that have just been stuck together. So if you know a lot of little pieces, you can multiply your vocabulary without having to memorise more. I would guess that I know at least as many Japanese words as English words, but it doesn't feel like it.
I will show you how to speak Japanese with almost no vocabulary at all, and then show you how to rapidly increase your vocabulary, and even guess Japanese words you've never even heard!
Reading & Writing
If you've never seen Japanese writing, it looks like this:
日本語は覚えやすい

The two sentences above should look the same. The first is Japanese text, the second is an image of that text correctly displayed. If they don't look roughly the same, you need to install Japanese fonts on your computer (here's some links to explain how).
So here is another big difference to Western European languages - Japanese has its own writing system that doesn't use the Roman alphabet like English. Surely this makes learning Japanese difficult?
Not at all. True, it's an extra thing you have to learn, but as you will see, learning the writing system actually unlocks the language, giving you free access to an enormous vocabulary, insight into the grammar, and most importantly for living & working in Japan, an understanding of what's going on around you.
This is an area I am particularly interested in, and I will show you how you can learn all 2000+ Japanese characters in as little as 3 months, while working full-time.
Listening & Speaking
Of course, speaking with Japanese in their own language is the whole point, and fortunately this is the easiest part. Japanese has less than half as many distinct sounds as English, and as far as English goes, it's on the low end of the scale anyway. So as a second language, Japanese has a distinct advantage over many other languages you might attempt to learn. There's only a few sounds which are not present in English, and they are quite easy to learn.
I will explain the real secret to achieving fluency in Japanese, and how to pronounce it like a native.