To learn how to write a sentence correctly, you must first learn the basic components of a sentence and the grammatical rules that determine how to organize those components. A number of English-learning resources are available online through free-english-study.com, Frankfurt International School, SkillsYouNeed.com and Trinity College of the Bible.
The arrangement of words in a sentence is known as syntax, and free-english-study.com and the Frankfurt International School website both offer explanations of the fundamental syntax patterns in the English language. The central element of every sentence is a subject-verb relationship, as seen in the sentence "Diana reads." This basic structure can be changed with the addition of an object, adjective, adverb or noun. For example, "Diana reads books" would be a subject-verb-object sentence, with the word "books" as the object. Free-english-study.com provides multiple example sentences for each variation on the subject-verb foundation, while the Frankfurt International School website explains how to build this foundation into more complex sentences.
Along with the principles of sentence construction, it is important to understand the grammar rules that help sentences flow together and make sense to the reader. SkillsYouNeed.com provides an extensive overview of English grammar, including explanations of verb tense, singular and plural words, articles, conjunctive words and contractions. The site also includes sections on proper spelling, punctuation and common writing mistakes. The Trinity College of the Bible website also offers a brief description of the most common syntax mistakes, such as run-on sentences, misuse of the comma and subject-verb agreement.