First, if you want really good yoghurt, you’ll want to thicken it. You can buy Greek style yoghurt at three or four times the price of regular, but why bother? Get some cheese cloth, plop your yoghurt into it, and let the water percolate out until it’s nice and thick. To sweeten it, I recommend using stevia concentrate. Stevia is an herb, the concentrate of which is hundreds of times sweeter than sugar, has no calories, and no side effects. This is what I use. A few drops is all you need. Alternatively, you can add honey to the yoghurt for sweetness if you don’t mind the calories.
For flavour, you can’t go wrong with vanilla. Real vanilla, not that awful “artificial vanilla flavouring” they sell in the supermarkets. If you have the time, you can make your own vanilla extract very easily for a fraction of the price you’ll pay at the store: buy a vanilla bean and drop it in a small bottle of vodka. Leave it for a month. Voila, you have homemade vanilla extract.
Any kind of fruit or berry preserves or compotes also go well with yoghurt. I’m partial to strawberry preserves, myself. If you want a very easy, simple way to make apple compote, peel an apple. Put it in the microwave until it turns mushy, then mash it with a fork. Voila, instant compote.