The impact of a copy depends not only on what is said but on how it is said. Words are very much powerful and as a copywriter, you should know how to make use of it to grab the attention of your target people. There is no fixed set of rules to write a great copy because with changing publishing medium and times, the attitude of prospective customers does change. However, it is better to write and explore what works and reflect on what does not. There are some basics mistakes which you need to avoid while writing copy.
The target people are more important than the advertiser. Keeping focus on the company and brand is the surest way to put off readers. People are interested in how your product and services can benefits then not in the company. So write copy while keeping your target audience in mind to make it attractive and beneficial to them.
To write a great copy it is important to send out the consistent message throughout. The body copy should match the message in headlines.
Suppose, if you are selling a luxury product, you target audience does not expect to get the product in cheap rates. If it is cheap, then it cannot be a product of luxury.
In the same way the copy, "New and Improved Hair Gel", contains conflicting message. The hair gel cannot be improved if it is new.
Copywriting is not about showing you mettle in the language and level of creativity, but it is meant to make the reader feel comfortable so that they can easily absorb the message and act upon them.
In an effort to sound professional, do not make your copy dull by using difficult language and write in passive voice. Inject life in your copy by writing in active voice and in conversational tone to get your reader keep reading and make them end up acting upon it.
Spelling and grammatical mistakes make your writing difficult to read and takes the attention of target people in a different direction. It is not only unprofessional to make spelling and grammatical errors, but it also ruins the impact of your message. So it is always best to proofread your copy to avoid any kind of spelling and grammatical mistakes.
Finally, the best way to avoid copywriting mistakes is to figure out your core message and target people, write your copy accordingly, proofread whatever you have written and then rewrite in a way that will elicit a desired response from the readers.