Start the ball off three or four clicks to the left. This should send it up the left chute and hopefully up to the top of the level. If the ball goes into the U-shaped enclosure it should dislodge some capsules for you to grab.
If you get stuck under the wall of unbreakable bricks, read these instructions on how to escape.
When I get the Gun on this level, I usually destroy some of the red bricks in the top left and right corners. I don’t bother destroying any of the unbreakable bricks from the bottom of the U — this doesn’t seem to help much and it gives the ball more ways to escape.