When it comes to the Star Wars original trilogy, the Imperial forces sure get a lot of flack for their aim. In fact, according to most Star Wars fans, the stormtroopers can't really hit anything. While that claim is well recognized in the Star Wars community, it isn't exactly true. The stormtroopers have actually killed quite a few people in the trilogy.
Star Wars: Episode IV - A New Hope
Tantive IV - 13 kills, 1 stun
In the very first sequence of the Star Wars films, the stormtroopers board a rebel blockade runner called the Tantive IV to clear the way for Darth Vader. In a brief shoot out, the stormtroopers triumph over the rebels, leaving 13 corpses and taking the rest of the ship hostage. They even shoot Princess Leia with a stun blast in only one hit!
Tatooine - 11 kills
When Obi-Wan Kenobi and Luke Skywalker come upon 11 Jawa corpses in the first act of A New Hope, Kenobi informs us all that stormtroopers must have killed them. They also later find the burnt bodies of Uncle Owen and Aunt Beru, but there are many theories out there claiming that Boba Fett was the one to kill them. Since I can't confirm or deny that, I'll only count the Jawas here.
Battle of Yavin - At least 2 kills
While many X-Wings were shot down by Darth Vader and Imperial forces operating the Death Star turbolasers, we did see at least 2 TIE fighters destroy some rebel fighters.
Star Wars: Episode V - The Empire Strikes Back
The Battle of Hoth - At least 20 kills
While the rebels might have escaped, the Empire definitely won the battle of Hoth. In the battle, we see 7 rebels shot down by AT-ATs, 3 snowspeeders get shot down (killing 5 pilots total), and eight other dead rebels later on. I'm sure many other rebels died in such a large-scale battle, but we see at least 20 on-screen.
Star Wars: Episode VI - Return of the Jedi
Battle of Endor - 11 kills
Sure, the Ewoks may have whipped the Empire's hide in this forest battle, but it wasn't without casualties. We see 7 Ewoks get shot down by AT-STs, as well as one rebel. Three other rebel corpses are shown later on, making a grand total of 11.
Death Star Assault At least 1 kill
More turbolasers shoot down rebel fighters, but at least one is shown shot down by a TIE fighter. But to be real here, with all of this fighting going on, I'm sure the stormtrooper kill count is significantly higher in this battle.
Grand Total = 58 kills, 1 stun
You see? The stormtroopers have hit their mark far more often than you may expect. I will say that the troopers have come down with "protagonitis" though. Protagonitis is a made up word that means that normal foot-soldiers cannot kill or harm main characters in stories.
For example, these stormtroopers can kill as many faceless rebel soldiers as they want, but when they are shooting at Han, Leia, and Luke, you can be sure they are going to miss. That doesn't make them bad shots, that makes them simple plot devices.