While one of the main features of academic writing in English is longer noun phrases, this does not mean that more words or more clauses in each sentence means better writing. Sometimes simple sentence structures are best for communicating complex ideas, and varying your sentence length is a more effective strategy than attempting to make your sentences as long as possible.
Readers tend to read until the end of each sentence before processing the information, so if there is too much information in one sentence, it may become hard work for the reader, or may hide the point you want to make. One way to avoid this is to make a conscious effort to vary your sentences based on length or number of clauses. Your thesis and topic sentences should be relatively short – although there may contain long noun phrases, they may often contain only one clause, because they each have only one point to make.
In addition, looking even more closely than the sentence structure, it is helpful to choose your words deliberately, and it is also helpful to alternate the use of simple words and elaborate words for the same concepts. This is where paraphrasing skills come into play. English usually has at least two words for the same concept, so it is often fairly easy to find an alternate word to use (search online for lists of synonyms if you need help). One option to consider is alternating between phrasal verbs and longer one word verbs.