To do any kind of revenue projections the best place to start is existing sales data from your own titles or similar titles in the same category. Obviously this isn't always easy to come up with but you can try sifting through the data NDP makes available on the net to see if there's anything valuable there.

The big things you're going to need are:

1. Market size (ie. # of targetable customers)
2. Typical # of units sold per title in that space. You can look at this for the "average" game but it's more effective if you look at it from the perspective of outliers as well.
3. Pricing model for your game and revenue % based on whatever publishing routes you're looking at.

With these kind of numbers you can come up with revenue targets that are worst case, conservative and best case.