You can vary your sentences in a number of ways. One way of doing this is to use the different forms of the same word. You have already learned that a word can exist in different forms (e.g. noun, verb, adjective, adverb, infinitive or -ing form). Knowing the different forms of a word is not enough. You must also be able to use these different forms in a correct sentence. For example, the verb persist means continue something despite some resistance. Persist can also be a noun (persistence), an adjective (persistent) or an adverb (persistently).
Study the following examples.
Despite frequent dope tests, some athletes persist in using performance-enhancing drugs.
Although there are frequent dope tests, some athletes show persistence in using performance-enhancing drugs.
In spite of frequent dope tests, some athletes persistently use performance-enhancing drugs.
Though athletes have to undergo frequent dope tests, some of them are persistent in using performance-enhancing drugs.
Note how the sentence structures change with a change in the form of the word persist.
Variety also comes from using different phrases and clauses. So if you are able to use many different word forms in a variety of sentences, you can easily alter your writing and impress the reader.