Openings

This past couple weeks, I have been struggling with coming up with an opening to my Work in Progress, and have changed it a few times and eventually went back to one that was a slight modification of the original, because I believe it sets up somethings later on better than the other versions.

However, my question is what are some of the most important things that have to be in the opening of a book?

My list goes as follows:

The main character has to be introduced.

The conflict should be introduced, but it can be hinted at as well.

I think the antagonist can be introduced as well, but not always.

The things that I can slow down an opening chapter is:

Excessive world building. It should be presented slowly, only showing us what we need to know to draw us in.

Excess backstory, we don't need to know every detail of the main characters right off the bat. I think this also works that we don't need detailed physical descriptions immediately. Slowly introduce it as the story unfolds, as the reader might have a picture in their head and you can build on that. If you do it all at the beginning you take away some of the imaginative fun for the reader.

What are some of your tips for opening chapters?