Writers: How do you exactly balance action and character development in your opening?

I try to start off with dialogue just before an action scene in the start of my story.

So the reader gets to see what the character is like then, bang...I drop them into the action.

For the reader to have some interest in the action its necessary that the reader is involved through the characters. So character development comes first and then whatever happens with the main character is up to you. It has nothing whatsoever to do with balance. This not mathematics... it is creativity.

I use the action to develop the character and show things about him. My guy has a very different reaction to someone punching him vs someone threatening his wife. He's pretty fearless on his own behalf, but he's terrified of her getting hurt, and her getting hurt because of him haunts his nightmares.

So, the character development happens in response to the action.

You need to interest the reader, but the action needs to make sense.

Action can develop parts of a character without exposition or history.

You've got 'lotsa' choices in this regard.

I try to describe him whilst describing the action.

e.g.

(The character's name) was plunged into darkness, a darkness which even his blue, cat like eyes couldn't penetrate. Suddenly, he felt something brush past his muscular, athletic legs, and his quick thinking brain instantly realised the crature at his legs. A shiver went down his long, visible spine.

I know this isn't a really good example, because I rushed it, but I think you get my point.