From Script Reader Pro, here is their No. 1 Hack on How to Introduce Your Protagonist to the audience.
Basically their advice is that the first time the audience (or script reader) sees the protagonist, he or she should be actively engaged in what they will be doing throughout the film, what the article refers to as "character essence". Here is a great example from the article:
How is Indiana Jones introduced?
Less skilled writers would've maybe chosen to introduce him at home talking to someone on the phone about the Ark. Or on a routine dig somewhere in a desert.
Sure, he's actively doing what defines him to a certain extent in these examples, but what shows us the character essence of what Indy's really all about?
Yep, being chased by boulders, dodging poisoned darts and leaping chasms clutching a precious golden artifact.
In other words it all comes back to the old screenwriting adage of show, don't tell.
Often, the action at the beginning of these films is completely unrelated to the eventual plot, but it's there in order to show us straight away who the hero is.
I found this piece of advice particularly interesting since aspiring writers are constantly told not to include anything that doesn't move the story forward. But there are exceptions to every rule, and setting the scene for the entire story to follow appears to be a very effective one. Imagine Raiders of the Lost Ark with Indiana Jones in that suit and those glasses in the classroom being the first time we see him, and the image it would have established in our minds, that this is a man of a buttoned-down academic world, rather than a man of death-defying action.
Opening with that action sequence also makes Indy relatable despite his larger than life heroics because we are shown that he has a flaw or weakness that pretty much everyone can understand: his fear of snakes.
Do take the time to read the whole article - it's really great food for thought. I know it's something that I'll keep in mind in the future.