I'm assuming you are doing these projections to raise money. If not, my advice won't be as applicable.
Build a model where you can change core inputs and they cascade through the model. That way you can change things quickly when someone says "Too low!" or "Too high!" to any of your core assumptions.
Have pretty, formatted outputs that you paste into slide decks.
Remember that you are building a sales document. As such, keep the intended customer and desired outcome in mind at all times.
You are trying to come up with numbers that justify your ask ($X at X% equity, $X Valuation)
So, look at other presentations (google) for disruptive companies and see how they framed the pitch.
Use as many concrete numbers as possible.
Look at the growth of public companies that disrupted so that you can back up your growth numbers.
If you are Uber, you grab numbers for how much money is spent on Transportation, not just taxi's. But, all the numbers are there for how much people spend on Taxis, Buses, Rental Cars, New Cars, Used Cars, and then some amount of pure, new usage.
This approach is lazy. "It's a $100B market, so if we just get 1% we are a Billion Dollar Company"
All you want to do is prove that the opportunity is semi-realistic and sufficiently large should you succeed. Or, that you can get acquired.
Build you valuation bottoms up.
This many users acquired per month. This much revenue per user, per month. This much churn. This Cost of Customer Acquisition. ETC.
Make sure these numbers can shift over time as you reach economies of scale and such.
How do you get there:
More important than the projections is your plan to achieve those projections
Milestones, activities, impact of those activities, team, financial/marketing/productivity leverage
How are you going to do what you say you will do
Why should I trust you? How passionate are you? Will you stick it out when it gets hard? Are you stubborn enough to see it through but humble enough to listen and pivot? Can you lead? Can you sell (customers and investors)
The projects are all pie in the sky.
What they are showing is a couple things:
-How you think. Realistic, Analytical, Thorough?
-How hard you work. This project is a plan and should translate into actual work. How much are you willing to work?
-How well you sell. You are going to pitch this thing
-How big the opportunity is. What the pivots might be
-What the risks are and the critical path, critical points of failure