You have to do this in one of the ten minute modes. The five minute modes will simply not be enough unless you have been playing this game for a rather long time. The one that takes place in the dark, I feel, is too hard, and should not be used. Start the game by grabbing a power dot and eating the four ghosts. rinse and repeat for the other three power dots. This should net you about two extra lives at least. After that, simply eat dots. Here are the biggest tips.
1) If you don't die, the amount you get per dot increases. See the "10" that flashes behind Pac-man when you eat a dot? That will go up to "20", then "30", "40", and "50". This translates to big points, and probably 20-30% of your score.
2) Although eating ghosts at the beginning of the level is reccomended, ignore them afterwards unless they are in your way. Use the power dots to simply keep the ghosts away from you while you clear dots.
3) Ignore the bonus points of the ghosts and instead go for the "food". The key, crown, etc, are above 5000 points, which translates to about an extra life per one eaten. Don't try to "taunt" ghosts over to you, and don't worry about "wasting" power pellets. Remember, you are going for score, which means going for the big food prizes.
I find Extra Mode 3 the best, as do many of the people in the comments below.
I had eaten about 10 of the highest food item by the end of the game, which translates to about 60,000 points just in that.
Remember, clear the boards fast, as in, as efficiently as possible, to create pellets and food faster.