Writers, rejoice! it’s perfectly acceptable to tell people what’s most important by saying “most importantly .” Many people were taught that using “most importantly ” or “more importantly ” was incorrect, especially when beginning a sentence. The scolders said that that “ly” adverb, called a sentence adverb, stood for “what is most (or more) important,” so adding the “ly” to the adverb was redundant. Why did it make sense to start a sentence “most surprisingly, it all ended well ,” but not “most importantly, it all ended well ”? No matter—if the teachers, or copy editors, wouldn’t let you use it, you couldn’t. But most happily, you can throw that shibboleth away.
In Garner’s Modern American Usage, Bryan A. Garner says that “writers needn’t fear any criticism for using the -ly forms; if they encounter any, it is easily dismissed as picayunish pedantry.” Using “more importantly for (what is) more important” is at Stage 5 on his Language-Change Index, meaning it’s proper English. And nearly every other usage authority agrees. The New York Times Manual of Style and Usage makes an important distinction, though: “Avoid this construction: He is tall. More importantly, he is young. Make it more important. The phrase includes an implied what is (What is more important, he is young). Thus important is an adjective modifying what.”
If you can’t figure that one out, don’t worry. It’s not important.