Avoid the Obvious
A thesis prepares the reader for what you are about to say. As such, your paper needs to be interesting in order for your thesis to be interesting. Your thesis needs to be interesting because it needs to capture a reader's attention. If a reader looks at your thesis and says "so what?", your thesis has failed to do its job, and chances are your paper has as well. Thus, make your thesis provocative and open to reasonable disagreement, but then write persuasively enough to sway those who might be disagree.
Bland: Dorothy Parker's "Résumé" uses images of suicide to make her point about living.
This is bland because it's obvious and incontestable. A reader looks at it and says, "so what?"
However, consider this alternative:
Dorothy Parker's "Résumé" doesn't celebrate life, but rather scorns those who would fake or attempt suicide just to get attention.
The first thesis merely describes something about the poem; the second tells the reader what the writer thinks the poem is about--it offers a reading or interpretation. The paper would need to support that reading and would very likely examine the way Parker uses images of suicide to make the point the writer claims.