You must be able to write clearly and correctly. You must be able to write to explain, to inform, or to persuade. You must also learn to write quickly. Law school and legal practice will require you to write often and under rigid deadlines. You should take every opportunity to work on your writing skills.
Oral communication is also an important skill of a lawyer.
The law student and the lawyer must be able to present their views and those of their client clearly, forcefully, and persuasively. You must learn to speak using proper English. All of us are sometimes lazy when we speak, and we often avoid complete sentences or use slang terms. The lawyer, however, will speak in formal settings where proper English is important for effective communication. This does not mean your speech has to be stuffy or boring.