The consistency - you can adjust the consistency of the froyo as necessary - if it's too thick to work with, add a little more lemon juice or frozen fruit. If it's on the fluid side, add more yogurt as desired.
Use frozen fruit - you can experiment with different fruit, citrus juice/zest and herbs here but the fruit needs to be frozen in order for this recipe to work - frozen berries work especially well but you could experiment with other frozen fruit such as mango, kiwi and melon chunks to see how you like the texture.
Serve Immediately - I mentioned this in the body of the post but it's important to serve this snack/dessert right from the blender for best taste/texture results.
The sweet factor - the amount of sweetener you add, if any, will depend on your taste preference but keep in mind that fruit is already quite sweet by nature and if you choose to use a flavored yogurt, you may want to skip the additional sweetener all together.
Why Greek Yogurt - I favor Greek yogurt for its exceptional protein content and gorgeous texture. All yogurts, regardless of milk fat content, begin the same way - by adding bacterial cultures to milk. Greek yogurt begins this way but it soon departs from other yogurt brands in that the milk is strained to remove the liquid whey. According to manufacturers, this process of straining means that as many as four pounds of milk are required to produce one pound of Greek yogurt. The resulting product is a far more concentrated source of protein (from casein) and a thick and creamy texture characteristic of Greek yogurt (regardless of fat content - even zero fat Greek yogurt has a cream-like texture reminiscent of sour cream - though I generally use 2% fat content). You will pay more for Greek yogurt but I think you will find that you get what you pay for.