Don’t start two sentences in a row with the same word.
An example:
“Yet despite his frustrations, he never established his own institution, even though his reputation would have allowed him to do so.
Yet since the 1990s, American education has been increasingly characterized by market-driven mentality.”
Go easy on “I” and “This” in the first sentence position:
Too much “I”:
“I will look at J.D. Salinger’s work in this diploma thesis. I will examine his life, along with the major experiences he had. I will then consider…”
Too much “this”:
“This diploma thesis looks at J.D. Salinger’s work. This body of writing will be examined with regard to his life. This approach…”
(This tips ignores stylistic and rhetorical repetition – such as that used in Martin Luther King’s “I Have a Dream” speech.)
More here: http://www2.arnes.si/~bjason/index.html#guides