Whatever it is, let this external element lead you into and support your internal conflicts. Also a well-structured external element will keep your heroine and hero together more. They want you to dazzle them immediately. Describing your heroine's dress or that lovely meadow across the street just isn't going to do it. Jump immediately into the conflict.
Internal conflict can lead to external or vice-versa.
Don't take your first fifty pages to tell the reader what happened ten years ago. If it's relevant to the inciting event of your plot, try to weave it in gradually. Chances are, we just need to understand that something in the past altered your hero or heroine. We don't necessarily need to see it. A developing friendship Don't assume we need to know everything about your characters by page 5.