Judging from the search strings that show up in my referrer logs, a lot of people come here wondering “Can I start a sentence with an adverb?”
Yes, you can.
For example, this sentence, beginning with the adverb slowly, is perfectly correct and clear:
“Slowly I turned.”*
As with adverbs placed anywhere else in the sentence, be aware that modifier placement can greatly change the meaning of the sentence.
In the example above, the adverb can only modify the verb turned. In longer sentences, there might be some confusion about what exactly is being done slowly. You might want to experiment a bit with it, just to be sure you’re really saying what you mean to say.
Sometimes, an adverb placed at the beginning of a sentence functions as a sentence adverb (also known as an adverbial disjunct), modifying the meaning of an entire sentence or clause. For example:
“Fortunately, I was able to avoid attending the Will Ferrell movie marathon.”
In this case, the speaker is saying that he considers it fortunate that he was able to avoid attending the Will Ferrell movie marathon.
Note that sentence adverbs can appear in the middle or at the end of the sentence, and they are set off from the rest of the sentence with commas. (For example: “I was able to avoid attending the Will Ferrell movie marathon, fortunately.”)
*500 bonus points to the first person who can identify this reference.