Avoid using the same conjunctions again and again. “But” and “as” are two main culprits here.
Showing contrast:
“The academic year is almost over, BUT that doesn’t mean I have stopped already. Some students are tempted to stop, BUT I am not. BUT this is not a desire that is limited to students.
Showing causality:
“AS the moon goes around the earth, and AS the earth goes around the sun, we can conclude that the moon goes around the sun. AS I do not have a telescope, I have to take this on scientific faith.”
Fresher:
“ALTHOUGH the academic year is almost over, it doesn’t mean I have stopped already. Some students are tempted to stop, BUT I am not. This, HOWEVER, is not a desire that is limited to students.”
“BECAUSE the moon goes around the earth, and AS the earth goes around the sun, we can conclude that the moon goes around the sun. SINCE I do not have a telescope, I have to take this on scientific faith.”
[“AS the moon goes around the earth, and AS the earth goes around the sun…” or “BECAUSE the moon goes around the earth, and BECAUSE the earth goes around the sun” would of course be pleasant parallelisms.]
Another note: starting with “Because…” signals causality from the outset. In other words, there’s none of the ambiguity that might spring from “As…”
“As I was walking…” can continue:
a) “…I was obviously not driving.” (causal)
b) “…down the street, I saw a duck.” (temporal)
All of the tips to date are available at:
http://www2.arnes.si/~bjason/LW%20tips.pdf