Many of us were taught that no sentence should begin with "but." If that's what you learned, unlearn it - there's no stronger word at the start. It announces a total contrast with what has gone before, and the reader is thereby primed for the change.
William ZinsserAbraham Lincoln and Winston Churchill rode to glory on the back of the strong declarative sentence.
William ZinsserMy commodity as a writer, whatever I'm writing about, is me. And your commodity is you. Don't alter your voice to fit the subject. Develop one voice that readers will recognize when they hear it on the page, a voice that's enjoyable not only in its musical line but in its avoidance of sounds that would cheapen its tone: breeziness and condescension and clichรฉs.
William Zinsser