Invest in your employees (train and level them up), fire the shitty ones to hire better ones, rotate your employees for the tasks (don't have the same person do graphics twice in a row; the same applies to sound, design, etc.), pump money into advertising, and pretty soon they will be making hall of fame games every time, which will sell like Hotcakes (Hotcakes is a motion control cooking game produced by Seki Systems, a gaming company in the long line of many that takes its name from a Japanese word in the game 'Go').
Find a game combination that is both popular and appropriate. For example, my Romance Simulator games are both extremely popular (both As) and an appropriate combination (increases their level). My long running Shogun series, which explores romance and intrigue in the Warring States era of Japan, includes 9 games, and the last four have sold 33 million, 41 million, 51 million, and 55 million copies. I've also had success with Online RPGs (Online Dreams 1 sold 21 million, Online Dreams 2 sold 42 million), golf simulators (Ninja Golf 1 - 7, the last sold 52 million copies), and many others.
Another thing: don't make the same game type twice in a row. Stick to a few different game types and rotate them. That way, you will increase fans faster. Also, when you initially start out, it makes sense to take contracts for cash and use the research boost option when developing games.
For my first couple of years, I put out really shitty games in popular genres backed by strong advertising, and my profits went up and up until I could afford to hire better people and train them to the point where every game I sold was a blockbuster. After I was selling between 100 - 150 game units a year, I had a 200 million dollar warchest, which I invested in a 64-bit BD-disc console (cost me 100 million dollars) while simultaneously spending 50 - 70 million dollars on advertising to shore up my fanbase. Protip: to build a console you need a hardware engineer. To get a hardware engineer, you need to level up someone in all jobs available. To do this, you need to use the 'change career' powerup that you can buy from the salesman.
Anyway, both of my consoles have dominated the market and by year 20 there was literally nothing left to do. My fanbase was approximately 999 on all categories, my games sold 40 - 55 million units each, and my console penetration wasn't going to get any better. The only thing eluding me has been the perfect score. I've gotten several 10, 10, 10, 9 scores. I dunno if you can get a perfect score. Got GOTY and won every other category though, so fuck the reviewers.