To improve making your sentences, you need to first keep in mind the length of the sentence, it should be too short nor too long..use words to join two sentences if they are closely related
use good and different words in the sentences,instead of simple and easy words

put the punctuation correctly.
the speech and tense should be correct

make the sentence understandable, dont make it complicated and confusing
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Improving sentence totally depends on the sentence structure, The making a sentence structure correct make the sentence more understandable and appreciative. But above that you have to understand one thing If you can make a sentence in 5 words do not try to make it 10 words. Like very short example : 

What is your name?
Ans : My name is Arjun. (if you say a sentence like this then its totally not impressive)

What is your name?
Ans: Arjun.

So try to make sentence short as possible its also try to put phrasal verb. Thats much more apprititable then using normal words. But between all of them remember to put correct tense and grammar. Read newspapers, Novels and Watch movies that helps alot. 
keep it short ,meaningful,lucid and take care of tenses and punctuation.atually u should be thorough with the syntax.