Even some native English speakers have difficulty understanding basic English sentence structure, which is usually referred to as syntax. If you don't understand English syntax, your sentences might not always make sense. You can't communicate effectively if others can't understand your sentences. Even if poorly constructed sentences make sense, they lack authority and reflect poorly on the writer's English skills. Once you mastered English sentence structure, you will make fewer mistakes when writing. Polished, error-free writing is easy to read and understand.
Purchase and study an English grammar book. You can find inexpensive educational books at thrift stores and used book outlets.
Study sentences you see in print. Look for the sentence's subject, which is a noun. A noun is a thing, often a location, person or idea. Often, the first word or group of words in a sentence is the subject, but this isn't always the case. Generally, in English, the subject of a sentence is who or what the sentence is about. In the sentence "John wrote a letter," "John" is the subject. In the sentence "Usually John sends email," "John" is still the subject, even though "John" isn't the first word in the sentence.
Look for a sentence's predicate. The predicate always contains a verb. Verbs describe what the subject is doing. In the sentence "John wrote a letter," "wrote a letter" is the predicate, and "wrote" is the verb in the predicate.
Learn to identify a sentence's subject by first locating the verb. For example, in the sentence "John wrote a letter," you'd single out "wrote" as the verb. Once you know what the verb in your sentence is, you can ask yourself who or what is acting on the verb. Using the same example, you would ask yourself "Who or what wrote the letter?" The answer would be "John," and "John" is that sentence's subject.
Practice identifying sentences' subjects and predicates. Read many simple sentences, which include a single independent clause, such as the two "John" examples. An independent clause contains a subject and a predicate. Circle or underline a sentence's subject and predicate as you see them.
Work with different types of sentences. Some sentence types include simple, compound, complex and compound-complex.
Learn to identify compound sentences. Compound sentences contain two independent clauses that are connected by a comma and a conjunction, such as "and" and "but." "John wrote a letter, but usually John sends emails" is an example of a compound sentence.
Learn to identify complex sentences. A complex sentence contains an independent clause and a dependant clause, which are separated by a comma. A dependant clause is a sentence fragment, which means it lacks a subject or predicate and couldn't stand alone as a sentence. "John likes email, which is more efficient." The dependant clause in that sentence is "which is more efficient," since that clause doesn't have a subject.
Learn to identify compound-complex sentences, which are a combination of compound and complex sentences. Compound-complex example: "John writes letters, but he prefers email, which is more efficient."
Take online English sentence structure quizzes, which are available at websites such as English Daily.
Enroll in an online or brick-and-mortar English class if you need help with advanced English sentence structure or you find that the principles still aren't making sense, even after repeated study.