Waiting until the battery is dead
As surprising as it may seem, it's best to charge your phone when the battery isn't dead yet. Why? Because it greatly reduces the life of your smartphone.
Using your phone while it's charging
If you use your phone while it's charging, it will tend to heat up and damage your phone over time. It's best to let it charge without using it.
Charging your phone as much as possible
It's best not to charge your phone to 100% if you can avoid it. Why? Up to 80% of the battery's cells are in "good condition", but the other 20% degrade more easily. This also explains why charging slows down as you get closer to 100%.
Charging your phone with a computer
According to a study, charging your phone using a computer lowers the original battery's capacity by 65%. Basically, an electrical outlet is your best bet!
In addition to these useful tips about charging your phone, we've also recently been made aware of why we should never borrow chargers from strangers!