Many students of Japanese just want to communicate. Sure, they want to say things correctly as often as possible, but they also want to get into the language quickly and start mixing it up early. This Japanese grammaris meant to help you do just that. It makes no pretense of being complete, but tries to pack the most useful information necessary to achieve the goal of using Japanese in the shortest possible space. This article therefore only covers one of the main obstacles, particles (those wa, ga, wo, de, ni and he thingies).
This is my reasoning on this: you can build a vocabulary of nouns, just by looking in a dictionary or asking a native speaker. They almost never inflect (in any true meaning of the word) and are easy.
Plus we won't be worrying about those strange noun-like things that can act like adjectives. So you can take care of the nouns yourself as you see fit.
On the other hand, the verbs and adjectives inflect so I'll try to present the most compact rules conceivable for allowing you to manipulate every verb you ever encounter and hopefully you can take it from their. The less mental overhead for remembering how to do it, the less painful it will be. After knowing the conjugation rules pat, you can get new vocabulary out of a dictionary or ask a native speaker. Now that you have a bunch of nouns and a bunch of verbs and adjectives (that you can inflect), you need to know how to piece them together. That's where learning about the particles come in. Remember, this is a quick guide so don't expect these generalizations to always work, just expect them to work in as many cases as possible based on what I know.
In the case of this guide, return comments such as: "You made generalization X, but for got to mention exceptions Y and Z." won't be appreciated very much. This is a quick guide, remember?
So be forewarned that there are exceptions all over the place, but that I have tried to be as accurate as space allows. And space is the primary concern here. Please don't forget that.