Why this is Important 

I am writing this sort of as a meta chapter because it's a problem I see in a lot of the books I review. Writers have this great nuanced world and complex character interactions and really well thought out plot that they clearly care about a lot and put a lot of work into

...and then they fail to make me care about it.

Why do people Read?

In order to put this into context, I'm going to take a step back and talk a little about why people read books--particularly fiction books--to begin with. Typically they're not reading to learn about this really cool world the author built. They're reading so they can vicariously experience a relatable emotion via the characters. They're looking for emotional investment, not things.

I'm going to take the opening three paragraphs of Harry Potter as an example:

Say what you will about Harry Potter, but this is a great opening. It's not a great opening because it conveys a lot of information (though it does). It's not a great opening because it sets the scene well (though it does that too).

It's a great opening because it introduces me to the Dursleys, then it immediately makes me dislike them. Their primness, their properness, their 'I must be better than you' airs are woven into every word they speak. I know people like this, and they annoy me. So the Dursleys annoy me too, because they look JUST like those people I've known in real life.

It gives me an emotional response to latch onto, which propels me forward until we meet Harry a few paragraphs later.

That is what you need to do in order for me to care about your piece.

So how do I do this?

Take a step back. Don't worry in the first paragraph about spoon feeding me every detail of your world. Don't even worry about that in the first page. You should give me a little information, yes, but more importantly, you need to give me an emotional response to what you're writing about.

Is your character happy? Sad? Lonely? Do they like the world they live in, or some aspect of it? Even better, do they really hate or feel nervous about something they're being exposed to? Put yourself in their shoes for a second, then show me what they feel.

Try to stay away from emotions like bored or tired, because they tend to be turnoffs for the reader. But give me some sort of strong response and I will immediately care about your characters.

It's all about relatability.

I need to be able to feel like I can understand the characters you're writing about and be able to put myself in their shoes. If you can do that, you've mostly won. You can get a lot farther on making the reader feel strongly about something, right away, than on describing every intricate detail of a world they don't yet need to know about.