Whats that you may ask? A language study plan is a guide for the approach you'll take in learning a new language. Many people approach the task of learning Japanese (or another language) in a very random manner, if you can imagine blindfolding yourself and playing darts you'll have a fairly vivid idea of both the nature of this type of learning and the type of success you can expect from it.
It is common for people to start with a phrasebook or picking words at random from a dictionary or a website. This is the dartboard approach where the L:earner just takes snippets from a whole number of places and tries to learn the language though memorization and repetition. This is one of the LEAST effective ways to approach your study as it offers you no context for understanding what you are trying to say. Instead of blindly throwing darts I prefer to think of Learning Japanese as cooking a cake or other delicious treat.
When cooking you start with a list of ingredients (Zairyou) that you need in order to make the cake. If you forget or neglect to use any of them the cake becomes lopsided or flavorless. It is the same with Japanese!
You start with an understanding of the basic elements of a sentence: particles, nouns,verbs etc. and then you build on this with an understanding of how to conjugate verbs and use grammar patterns.
Once you understand these simple principles you gain an ever increasing level of fluency with each new grammar pattern. This is because instead of memorizing a sentence and knowing how to say only one sentence you can change parts of the sentence easily to say a whole host of other things! Your Japanese will develop much more quickly than if you just try to memorize the 3500 words its estimated that a person uses in their average vocabulary.
Your language study plan can be simple or complex based on how much time you have available, but with even 15-20 minutes a day you can make significant progress. For example for the 2 years that I spent in Japan I would do the following:
Sam's Lesson Study Plan
1) Study a grammar pattern for 10 minutes in the morning
2) Write out 10 words on a card with their English and Japanese translation and meanings, then I'd go over them before I left for the day.
3) That day when I was out and about would use the daily words and grammar pattern as often as I could in all its different variations. I'd find reasons to use the words I had studied as this makes it easiest to recall them, that way if I was using them incorrectly in speech people would help and correct me.
4) I'd review the grammar pattern and words again before going to bed, this helped them really sink into my long term memory. Once I started doing this I found that I remembered 8 out of 10 words a week later instead of 4-5 out of 10. A large increase.
I hope this helps you with your goals to learn Japanese, the key to a great Language study plan is KISS (Keep it Simple Stupid) the easier you make it the more often you will do it. If you design a 3hr course of study for every day You'll never actually sit down to do it!