Star Wars SPLINTER OF THE MIND'S EYE by Alan Dean Foster

The fun of this novel is knowing that it was published in 1978, right after the first STAR WARS movie, A New Hope, and before the second, The Empire Strikes Back. At that time, no one knew Luke and Leia were twins seperated at birth. "Dude, you kissed your sister, ewwwww!" And no one knew Darth Vader was their bad daddy. He was just a really powerful bad guy in a black suit who had it in for Obi Wan Kenobi.
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Princess Leia gets to fly her own fighter in this one, which was kind of cool. She's on her way to a diplomatic conference. The Rebel Alliance won a major victory when they blew up the Death Star, but it's still a lot of work to hold it together and try to build it up enough to take at the Emperor.
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Luke Skywalker volunteers to escort her in his X-Wing. They run into some kind of energy barrier and crash-land on a mining colony. They go undercover to try to find a way off and/or to contact help. Unfortunately, Princess Leia has a hard time playing the part of a haggard minor and Luke's Force-sensitivity draws the attention of Hala, an old woman who happens to be Force-sensitive too. She's not a Jedi or anything, just Force-sensitive. Hala offers to help them find a way off the colony if they'll help her find the Kaiburr chrystal. She gives Luke a sliver of it and he realizes how it focuses the Force. Leia agrees they must find it to keep it out of evil hands.
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The threesome leave the bar they met in and Luke and Leia get into an adolescent scuffle. Well, you know, they are only about 19 or 20 years old. Their scuffle draws the attention of a couple of local baddies and before you know it they're all thrown in the slammer for disturbing the peace.
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Okay, no big deal, but the officials learn about the chrystal sliver and decide to hold onto them a little longer and ask the governor about the chrystal. The governor suspects Luke and Leia are not mere thieves and the race is on before he realizes he's the guy who blew up the Death Star and she's an Aldoranean princess, a leader in the Rebel Alliance.
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If you've read Star Wars novels before, you know some are good and some are, well, not so good. It's an enormous challenge to write a truly great novel using characters someone else created. I thought Luke, in this one, wasn't consistant with his level of character development at this point in the Star Wars timeline. However, it was still really interesting to read this flashback and chuckle about how it relates to everything else which has happened in the Star Wars universe since. Being an old release, you should be able to find it in any good-sized public library.