First of all, you should know the basic rules of the Russian language, they just need to memorize. Some materials on the rules of the Russian language you can find here: http://www.gumfak.ru/russian.shtml
Knowledge of rules is necessary but not sufficient condition for competent writing. A competent person may not remember the rules that he once taught in school – he just knows how to write. To achieve this "congenital" literacy, it is necessary to read quality literature. The correct construction of sentences, punctuation, spelling words the classics of Russian literature must be deposited in the mind, become a kind of template.
A wonderful example of Russian writing is the work of Konstantin Paustovsky. If your home library does not have his books, download their electronic versions in one of the network libraries.
Reading books Paustovsky, listen to the sound of speech classic. Its melodiousness, melody, rhythm. The correct writing is akin to poetry, should flow smoothly, slowly, with pauses in the right places, emphasizing its rhythm. The correct rhythm of the text is the basis to competent writing.
Start to learn the proper rhythm with writing simple phrases of a few words, then match these phrases. For example: "it was a fine spring day. A mild breeze would carry the smell of acacia blossoms". First, combine these sentences without a comma (which is wrong): "it was a fine spring day, a mild breeze would carry the smell of acacia blossoms". According to the rules, these sentences should be separated by commas, as each has a subject and predicate. But if you just listen to the rhythm of the phrase, then catch a break in that place where there should be a comma. Learning to feel the rhythm of the phrases, you'll be able to correctly place punctuation without thinking about the rules.
To master the rhythm, listen to audiobooks. Listen to how the narrator pronounces the phrase where it makes a punctuation pause. When you write your texts, listen to their sound and put the commas in a logically flowing from the rhythm sound.
Use of programs-simulators, which allows to increase literacy written speech, you can find them on the Internet. These programs allow you to test different aspects of literacy, it is possible to choose difficulty levels. Having worked with similar programs, you will be able to significantly improve the quality of writing.