Model S has one of the most sophisticated battery systems in the world. The most important way to preserve the Battery is to LEAVE YOUR Model S PLUGGED IN when you are not using it. This is particularly important if you are not planning to drive Model S for several weeks. When plugged in, Model S wakes up when needed to automatically maintain a charge level that maximizes the lifetime of the Battery.
There is no advantage to waiting until the Battery’s level is low before charging. In fact, the Battery performs best when charged
Note: If the Model S Battery becomes completely discharged in a situation in which towing is required, the owner is responsible
for towing expenses. Discharge-related towing expenses are not covered under the Roadside Assistance policy."
Just don't set your charge limit any higher than 80%. There's also really no advantage to setting it lower.
I think the important thing we can share with our fellow inexperienced owners, is that they can read the manual online, or download the PDF to take with them on a mobile device. Some might not know this, and might not be able to sit in the car for long durations reading the manual.