The high-level answer as you can't.
Sales encompasses many aspects and techniques that you can "learn" (as in being able to do rather than just knowing only through practice). When you are selling, the emotional/human factor influences every single aspect of a sale and therefore you need experience to find the best strategy but then be able to adapt tactics on the fly.

However, to give you something useful, you should pick one or two of the elements of sale, and read about them. Depending on your product/market/channel, you will be able to pick form different pools.

I personally like negotiation and price psychology.
Another great thing about sales is that it doesn't have to be about making an actual sale. You can abstract the teachings and apply them to everyday life with much more casual interaction you can use to practice.

Happy selling!