Having been around the forums for a while now, it seems one of the more common mistakes newcomers make is starting out with a massive project in mind. Think simple.
The other biggest mistake that newcomers make is thinking that they will get rich. I will admit, I did not think that it would be as hard as it has been when I first started. However, I have been around startup companies enough to see the 2 year/5 year rule in effect (#1 in my advice post above). I was a consultant in one of those startup companies. They had the backing of three venture capitalists to start up. Some time in year two, there wasn't enough money to pay the employees. I actually worked for free for 3 or 4 months. Finally, I left. About six months after I left, the venture capitalists all pulled out and the company was gutted. It was surprising because they had a really great idea. Unfortunately, the starting materials were bad and they could never take it all the way to a finished product.
Long story short, even if you have a great idea, you might still fail. It happens. Even though I have revenue right now, I might still fail. It is just the way the business runs. I don't have any data to support this, but here is a rough guess on how indie developers fair:
1. 0.01% of indie developers become millionaires. This seems more based on a game going viral or faking 10,000 downloads to get started (like flappy bird allegedly did). If you go wild spending money without making any new products, I suppose you could fall into #2.
2. 1% of indies make a significant amount of money. I do not know their exact financials, but I think AdventureIslands and Colburt's gang fall into this. By significant, I mean enough to pay rent/bills and still have more money left over to play around with and/or hire out work. If you play your cards right and work really hard at expanding your business, you could eventually move up into #1. Your revenue might hit a dry spell also and drop you into 3.
3. 10% of indies make enough to survive. This is where I fall in. It basically means you can pay rent and eat, but not much else. Trust me though, this is still an amazing category to fall into as an indie
Just keep backup plans in mind if the revenue stream dies. Hopefully this is just a phase for your business and you can move up into #2.
4. 50% of indies make some money, but still need to find employment elsewhere. Having a full time job and making some money on the side from video games is still awesome. It simply means that you might not be making games all of the time. If you are doing full time indie and fall into this category, make sure you have backup plans or enough money in the bank to cover expenses for a while. Start thinking outside of the box for ways to make money as an indie. Talking to local business (like what jorannpe did) or your town's officials (like TheIndieStation is doing) is a fantastic idea.
5. The rest of indies make next to nothing. Although, you might still make enough to cover production costs/subscriptions. If you fall into this category, that is fine. Just keep making games for the fun of it. The pitfall of starting out with big projects when going full time indie is that you might fall into this category and not even realize it for a few months or years. I was in this category for my first 9 months as a full time indie (although I did take 3-4 months off for family matters shortly after starting). Now looking back, I am glad that I snapped out of my stupor.
Super Meat Boy seems to be the go-to for newcomers expecting to make millions. Keep in mind, McMillen had been developing for 8+ years and Refenes for 9+. It still took them almost 2 years to develop the game (even though the Indie documentary covers the last 6 months). They also had Meat Boy as a starting prototype and initial fan base. To be fair, I also used Indie Game: The Movie as inspiration to start developing. The difference is that I did not look at the sales figures for inspiration. Instead, I saw how passionate all of the developers were and I wanted that in my life.