Since you are pre-revenue, you are guessing. It (hopefully) is educated guessing, but in the end you are making a best-case projection. So you need to be able

Since you are pre-revenue, you are guessing. It (hopefully) is educated guessing, but in the end you are making a best-case projection. So you need to be able to back up whatever assumptions you can use. For example, some reports have mobile ad revenue growth up between 70-100% y/y. So, I'm guessing your main revenue drivers are going to be the price points, market penetration, and the amount of repeat users/churn (depending on if it's a SaaS revenue model or not). It's hard to give you much more without some more information, but in essence figure out how much of the market you can capture per month, how much you charge for those, and how many people reuse/stick around each month. And then do a low/high case as well. It's unlikely any of these will be close to the eventual truth, but you'll at least understand the drivers. If you are asking what the numbers should be...well, that's your job as the guy with the product. :)