If you are a graduate student in any discipline, you may need to write papers and those papers will normally be formal or academic discourse. Every library reference section has many books devoted to this style of writing. In general, your ability to write academic or formal discourse in English will determine your grade level in a course. Much of the formal instruction in grammar has disappeared from American middle schools and secondary schools. At one time in the 1960’s the National Council of English Teachers elected NOT to teach grammar anymore. Part of this was due to the impact of linguistic study on the discipline of learning grammar. Whatever the reasons for this abandoning the bedrock knowledge of a language, it has left an ever expanding hole in the study of English.
One of the reasons that it has had an impact is because of the difference between language acquisition and language learning. Native speakers acquire their understanding of their language from birth. Acquisition does not include learning the grammar of that language in a formal way. Look at the definition of grammar from several sources to see how important it is to learning any give language:

In the Cambridge Grammar of the English Language, on page three it says:
A grammar of a language describes the principles or rules governing the form and meaning of words, phrases, clauses, and sentences. As such it interacts with other components of a complete description: the phonology (covering the sound system), the graphology(the writing system, spelling and punctuation), the dictionary or lexicon, and the semantics. (CGOE p. 3)

The conclusion of this statement of grammar, on Page 4 says:
A grammar itself is divisible into two components, syntax and morphology. Syntax is concerned with the way words combine to form phrases, clauses and sentences, while morphology deals with the formation of words.
From this description of grammar, it is easy to see that grammar is an essential part of learning a language. Most second language speakers understand this from the beginning of their study of a language. Everything about a language involves grammar. A language has no structure, no defining element without the acceptance of grammar itself as a part of that learning.
The basis for all academic discourse lies in the fundamental ideas of learning, examining and understanding. As Socrates told us, “an unexamined life is not worth living,” he was telling us to examine every idea again and again. There is always a truth lying beneath a stated truth. A true scholar will find these truths as he or she lives out their lives. Academic discourse states these truths and this research with succinct writing that expresses your ideas as straightforwardly as possible. Academic discourse requires correct spelling, good grammar usage and a serious approach to the subject or idea presented. 
The idea of examining our thoughts, seeking truth wherever it is found and pursuing knowledge wherever it can be found is the essence of critical thought. Guides that take us to good academic discourse are found in many places. For English some of these are Strunk and White, The Elements of Writing. It is a book that most people find will teach them something new every time you open it. It is found on the Internet at: http://www.bartleby.com and other literary websites. There is at least one electronic version available and almost certainly will be a Kindle version published by http://www.amazon.com in the near future.

• The Modern Language Association, founded in 1883 in the United States seeks to guide academic and writers in general on good usage in academic discourse. www.mla.org

The Chicago Manual of Style is written as reference for newswriters, scholars and anyone who wants detailed information, examples and rules for writing. http://www.chicagomanualofstyle.org/home.html.

• The Cambridge Grammar of the English Language, is a comprehensive and detailed reference on grammar in the twenty-first century. It is the work of many scholars with twelve authorial scholar’s contribution to the grammar of English. A significant change in the Cambridge’s approach is the acknowledgement of the more favorable choice of descriptive presentation of rules, rather than the prescriptive approach used for many generations of scholars. More about this book at www.cambridge.org/uk/linguistics/cgel

• The Oxford English Dictionary is no longer restricted to library visitors and a somewhat truncated version can be found on CD-ROM that can be installed on a computer.  This is the definitive lexicon of the English Language. It provides detailed etymologies of most words, comprehensive definitions and references to indicate historical usages. Most other English language dictionaries are guided by the OED. www.oed.com

The Merriam Webster Online Dictionary is an extension of the Merriam Webster Collegiate Dictionary published in 2003 and available at http://www.merriam-webster.com. This dictionary provides computer generated sounds to pronounce words in standard English.
As a new learner of English, keep in mind that you are trying to learn to speak, read and write the English language for the most practical reason: to broaden your understanding of the world through language. With that in mind, remember that, for new learners of English there is no language called British English, American English, etc. The only language that you should concentrate on in speaking, reading or writing is the English language, nothing more, nothing less. All accents are mispronunciation of the standard words.
British English, even British Received Pronunciation is a variance from the words described in dictionaries. American English varies from state to state, city to city and even neighborhood to neighborhood because of ethic and economic variations of the population. All of these, including twenty-six or so regional dialects in England and more of the United Kingdom, as well as all of the American dialects are not what new learners need to speak, read and write the language. Why is this so? It is because you may never speak to a native English speaker in some parts of the world. The pronunciation you use that is closest to the standard pronunciation of English words will be closest to what most people learn when they learn English.