As pgmco stated since the industry is pretty competitive it's always a good idea to price the software at a good value to increase the chances of more people making purchases and talking about it which leads to further sales. However, if you have a groundbreaking product then you should really spend some time thinking about price points, ect. It's somewhat a guessing game and until the software is released it's hard to tell what customers will value it at.
If there was a perfect sales plan for any product in any industry, then it would violate the nature of economics. Essentially what you want to do is bring the most exposure to your product for the lowest cost.
In my experience with software, the most successful companies offer freeware as what's known as a "leader product." What you want to get out of this leader product is brand exposure, product exposure, and company exposure. If your product is really hitting it off with the public then you can seek to diversify your product line and charge for new products, while still keeping your original product freeware. You may also consider charging for your product once it's successful.
It all really depends on the nature of what you're offering and what kind of business plan you have. There's many ways to approach a sales plan. Finding one that works for you will take a lot of trial and error. Best of luck to you.