As Toast messages are totally based on activity either created(displayed) by users action or background action/processes. It is best practice to show/display them in a way that users eyes do not have to roll all over the screen.
The Best Locations:
- Top-Right : Created usually because of users action.
- Top-Center : Created usually because of users action.
- Bottom Right : Created usually because of background processes/activity, advertising, chat pop-ups.
- Anywhere else - Less recommended, as we are just talking due to users action.
Above discussed locations are ordered based on priority from high to low
There are few among many examples i would like to share and are really worth.
For more check here
Hope! You get what you were looking for.