If you don't plan to add fresh or frozen fruit when you serve the muesli, you might want to add another sweetener, such as a drizzle of maple syrup.
This is just a base recipe. You should always start with the oats, but after that, feel free to change up the muesli ingredients. Try to go for variety: something to add crunch, something to add fat, something to texture.
Another great addition to muesli is dried fruit such as raisins, craisins, or goji berries.
When serving, I prefer to use frozen blueberries over fresh because they're cheaper and the berries are denser, creating a deeper and sweeter flavor. That said, I've used fresh blueberries before, and it still tastes great!