Effective sentences can be short or long. Short sentences provide emphasis and are easier to read. Longer sentences are appropriate when an idea requires elaboration. Generally, the most effective sentences contain no more than two or three clauses. When writing paragraphs, you will often find the balance and flow by varying sentence length.
For your writing to be effective, you must form sentences that express your ideas clearly and persuasively. Reread your sentences to make sure they transition well from one to the next. Make sure your sentences are complete with subject and verb. Eliminate any words or phrases that might be problematic for the reader.
Aside from writing the same word back to back, the most obvious example of redundancy is using words that mean the same thing. In writing, repetition can sometimes provide continuity. Does the repetition in your text help link ideas, sustain rhythm, create emphasis, or prevent confusion? If not, leave it out. Consider whom you are writing for and what you are trying to accomplish.
When a verb is in the active voice, the person or thing performing the action is the subject. Active voice helps readers visualize the action of a sentence. Active-voice sentences help readers visualize the action and are more direct than passive-voice sentences. Consider rewriting your sentences in the active voice. For example, instead of The cat was eaten by the dog, favor The dog ate the cat.
When writing a text in a formal context, avoid using slang words or colloquialisms, such as bro, gonna or whassup.
Ask yourself if your tone is appropriate for your audience and the goal you are trying to accomplish.
Not every word is effective in every context. Given your purpose and audience, choose words that express your intent. Reread your text and try to eliminate complex words, misused words, words with unwanted connotations, unclear pronouns, and clichés.