I enjoy iced coffee occasionally. It's best to start with a freshly cleaned brewing reservoir to remove the bitter-tannin build-up from daily brewing.
When I make it, I start with a good flavored brand. I make a pot and pour into a glass jar with lid and let it cool on the counter a bit before placing in the fridge.
When completely cooled, and ready to serve, pour over ice with your favorite flavorings as needed.
You mentioned that your attempts made it too bitter. Perhaps you could tweak the amount of coffee you use, or add more water to dilute.
Peace.