Make your texts more interesting to read by varying the sentences you write. If sentences are constantly of the same type and length, and with the same openers, the text will be monotonous and either too simplistic or too complex, so aim to write different types of sentences that are of different lengths and have different openers.

• Sentence types
  
  There are four types of sentences in English: simple, compound, complex and compound-complex.
  
  
  • Simple sentences consist of one independent clause (that is to say, at least a subject and a verb and, perhaps, an object, complement or adverbial).
    
    

    Slavery was officially abolished in the United States in 1863.

    
    
    
  • Compound sentences consist of two independent clauses joined by a conjunction (and, or, so, but, etc.).
    
    

    Slavery was officially abolished in the United States in 1863 but was still widely practised until the end of 1865.

    
    
    
  • Complex sentences consist of one independent clause and one dependent clause linked by a subordinating conjunction (when, if, because, since, before, although, etc.).
    
    

    Although slavery was officially abolished in the United States in 1863, it was still widely practised until the end of 1865.

    
    
    
  • Compound-complex sentences contain more than one independent clause and at least one dependent clause.
    
    

    Although slavery was officially abolished in the United States in 1863, it was still widely practised until the end of 1865 and racial bias still pervades American society today.

  
  
  
• Sentence length
  
  Well-written texts are made up of sentences of different lengths: short, medium and long. If you write too many long sentences, readers may feel overwhelmed by the excess detail and be unable to identify the important points. If you write too many short sentences, readers again may be unable to identify the important points and your text will sound childish.
  
  
• Sentence openers
  
  Sentence openers are any structures in the initial position of a sentence. They can give writing greater sophistication and help maintain readers’ interest. In his book The Craft of Scientific Writing, Michael Alley defined seven different types (Alley, 1996).
   
  
  • Subject-verb
    
    

    Slavery was abolished in 1863.

    
    
    
  • Prepositional phrases
    
    

    In the Deep South, the Ku Klux Klan was set up as a vigilante justice system in 1865.

    
    
    
  • Transitional words
    
    

    However, the organization was suppressed in 1872.

    
    
    
  • Introductory subordinate clauses
    
    

    Although the Civil War led to the abolition of slavery, it did not change the basic power relations between African Americans and whites.

    
    
    
  • Infinitive phrases
    
    

    To fully understand the influence of racial bias on the 2016 election, we measured anti-immigrant sentiment and racial resentment separately.

    
    
    
  • Participle phrases
    
    

    Summarizing the work of numerous political scientists, the author claims that the decisive factor in the electoral victory was racial resentment.

    
    
    
  • Verb
    
    

    Note that the victorious candidate never distanced himself from the opinions of white supremacist leaders.

    
    To see the importance of sentence type, sentence length and sentence openers, take a look at the following text (from Alley, 1996), in which there is very little variety.
    
    

    Mount St. Helens erupted on May 18, 1980. A cloud of hot rock and gas surged northward from its collapsing slope. The cloud devastated more than 500 square kilometers of forests and lakes. The effects of Mount St. Helens were well documented with geophysical instruments. The origin of the eruption is not well understood. Volcanic explosions are driven by a rapid expansion of steam. Some scientists believe that the steam comes from groundwater heated by magma. Other scientists believe the steam comes from water originally dissolved in the magma. We have to understand the source of steam in volcanic eruptions. We have to determine how much water the magma contains.

    
    
    All the sentences are of the same type (simple), all are of approximately the same length (short/medium) and all open in the same way (subject-verb). This means that readers pause at very regular intervals and the greater stress that is naturally given to the subject falls in exactly the same place, thus creating an extremely monotonous rhythm. Now compare it to the following revised version.
    
    

    Mount St. Helens erupted on May 18, 1980. Its slope collapsing, the mountain emitted a cloud of hot rock and gas and, within minutes, the cloud had devastated more than 500 square kilometers of forests and lakes. Although the effects of the eruption were well documented, the origin is not well understood. Volcanic explosions are driven by a rapid expansion of steam and, recently, there has been considerable debate over the source of this steam. Is it groundwater heated by the magma or water originally dissolved in the magma itself? To understand the source of steam in volcanic explosions, we have to determine how much water the magma contains.

    
    
    The revised text above has a much more varied rhythm because it exploits the variables of sentence type, length and opener. The first sentence is simple, short and has a subject-verb opener. The second sentence is compound, long and opens with a participle phrase. The third sentence is complex, medium length and opens with a subordinate conjunction. And so on.