Disclaimer: best is a subjective term, in this tip this term refers to central, busy, posh, active and safe zones of any city. for some people best might be a rural or quiet zone close to nature / mountains etc ..
The process is simple, launch google maps and search for the following:
- Posh/five star hotels
- Starbucks Cafes
- Apple store
in almost every city those landmarks are situated in or close to the best/happening areas.