How do you put in necessary back-story without losing your reader who wants to move forward?

Well, instead of using an info dump, I think you should use an info dribble. Just like it sounds. Little bits of info here, and little bits of info there.

Look again at the bit of reportage we made up for the last article on this topic:

John was a year younger and a couple of inches shorter than his sister, but both were dark with almond-shaped eyes and built like typical Aleuts—squat and strong. The Aleut people had settled the Aleutian chain some 4000 years earlier. Frozen corpses had been found intact, which showed the bone structure peculiar to the race and it had changed very little in the last 4000 years. Their work had changed very little, too. They still lived off the land on a diet that consisted of mostly fish, caribou, and moose meat. In some areas they ate seals and in other areas, whales. They ate whatever Mother Nature served up just as they had been doing for the last 4000 years.

"Hey," John said when he saw Nate. "Let's go to the gym and shoot hoops."

What do we really need out of that? What's important to tell so the reader will understand the characters and their environment and their predicament?

I want to tell the readers what Aleuts look like. I want to tell them the Aleuts have lived on the land for thousands of years. And I want to tell readers that the life is challenging and Nate can't just run out to Mickey D's when he's hungry. If I can get those things across, I think the reader will understand my character and his story.

So I'll start with two characters standing side by side, John and his sister. It's probably OK to use one sentence to discuss their physical descriptions.

John sauntered out of the house and handed Connie the lunch bag. He was a year younger and a couple of inches shorter than his sister, but both were dark with almond-shaped eyes and built like typical Aleuts—squat and strong. They piled onto the snowmobile behind Nate.

Then I'll move on with the story. The kids ride the snowmobile to go check the trap line. After a while I can dribble in a little more info.

Nate let off the accelerator and said a quick prayer, when he saw the tree, which marked the first trap on the line. He needed a wolf today as badly as his grandfather had ever needed one, or his grandfather's grandfather before him.

Not because he was starving the way they often were. He needed a wolf to appease his boozing uncle. It was important, when Uncle was drinking, to have a gift to offer upon entering the house.

As he drew closer to the tree, though, he could see that the trap was empty.

Now I've established that Aleut people have a certain physical appearance and that they people have lived there for generations (speaking of the grandfather's grandfather). All that's left is to make a point of the subsistence lifestyle.

So after passing by a couple of empty traps I can bring Nate to one with a wolf in it.

He aimed and squeezed and the wolf dropped.

"Nice shot," John said.

Nate nodded. He was thankful to be living in the days of snowmobiles and rifles. His grandfather had told him stories about times the people were so hungry they ate animal tracks left in the snow, hoping for some sustenance. Nate had never been that kind of hungry. He still relied on hunting and fishing to fill the dinner table, but it was a whole lot easier to manage with a rifle than a spear.

He moved the wolf with his toe, checking for signs of life. It was a big, shaggy, silver male. That was good. That would buy a night of peace at home.

So I've conveyed all the information I wanted to convey, but I did it in the middle of the action. I took out the one-paragraph history lesson and replaced it with several paragraphs, but the newer version, with the facts dribbled in as part of the story, is much more interesting. Instead of speaking about unknown Aleuts who have lived off the land for thousands of years, I spoke about Nate's grandfather. By doing that I give some of Nate's personal history and I tell something about what stories have shaped him and how he views his world. Because the history lesson now relates to Nate personally, it belongs in the story. It characterizes him and it contributes to his conflicts and their resolutions.