Language begins orally. Long before children learn to read and write they learn to speak. Thus, most people are more capable of recognizing grammatical problems when heard than when read. What's more, when reading the mind is amazingly capable of correcting problems--typos, missed words, spelling errors--so quickly and effortlessly that the conscious mind doesn't even notice. An easy way to identify grammar problems, then, is to read your writing out loud. Reading aloud allows the writer to hear his own words. Notice when the tongue trips over a sentence, as this often indicates an awkward sentence, which may also indicate a grammatically incorrect sentence.
One of the most common grammatical mistakes occurs when the subject of a sentence doesn't agree with the verb of the sentence. Agreement, in this case, means that the verb in the sentence hasn't been conjugated to accurately reflect the subject. Conjugation of verbs is something that develops naturally during language acquisition. By the time a child is 5 she knows, for example, that the verb "to be" must be changed depending on if the subject is singular or plural:
The car IS in the driveway.
The cars ARE in the parking lot.
However, things become more complicated and errors occur when the subject of the sentence is less obvious. The writer, then, must learn to identify the subject. The Capital Community College Foundation describes the subject of a sentence as the "person, place, thing, or idea that is doing or being something." So, in order to find the subject of the sentence the writer must first find the verb and determine who or what is performing the action are who or what is taking on that identity. For example:
The owner of the cats bought a litter box.
The verb in this sentence is "to buy," and the person performing this action is "the owner." Thus, the subject of this sentence is the "the owner."
A run-on sentence is another common grammatical problem and occurs when two or more independent clauses are strung together without the appropriate punctuation. ("Independent clause" is another term for a complete sentence.) The University of North Carolina at Chapel Hill provides a tool for identifying run-on sentences. If the sentence can be turned into a logical yes or no question, the sentence is probably not a run-on sentence. For example:
"The cat ran away," can be changed to "Did the cat run away?" a question that can be answered with yes or no.
On the other hand, "The cat ran away the dog chased it" cannot be changed into a logical yes or no question and thus indicates a run-on sentence. Run-on sentences can be fixed by either separating the two independent clauses with a semicolon, a period, or by using a comma with a conjunction.