Ever since the release of IT:Chapter Two, people are ecstatic and excited to watch what happens after the conclusion to the first movie, It: Chapter One. 

Some people have watched the second film, skipping the first movie entirely. It would be such a boneheaded move to just skip the first part of IT and watch the second movie first.  There are a multitude of reasons to not skip the first movie of the franchise.  

One reason to not skip the entirety of the first movie, is because Pennywise’s actions and the origin of the conflict would be lost.  The characters from the first movie reunite to find a way to stop the mad clown from terrorizing and killing every child in the town of Derry.

You also skip character development in between the two movies and this would be tough.  Many characters have changed personalities and relationships throughout IT: Chapter One that translates over into IT: Chapter Two.

Overall, if you are planning to watch IT: Chapter Two, you should plan to watch the first one before doing so.