Well, most of the time it will be an -ing form, if you do start the sentence with a verb-form.
When a verb is made into a gerund, it therefore functions as a noun and can be the subject (for example). This can also make the whole clause work as a noun.
eg. "[Getting up early in the morning] is difficult for me."
It can also start a sentence if the -ing form starts a participle phrase.
eg. "[Looking at the map,] I decided to head west."
Still, it is possible to start the sentence with "to (verb)", so pay attention. ;)