The short answer is to look for places where there are plenty of new jobs about to be created.
Stay far away from where jobs are or have evaporated and population is going down. Where? Like Detroit, Michigan USA. Both rents and property prices have fallen off a cliff.
It is up to you to find places where (for instance) new factories, mines, pipelines are going in. Ideally, you will get in early before the crowd, make your leveraged investments, and move on to greener pastures in a few years. Once the shills are selling a place as an “opportunity” it is too late.
Years ago Staten Island (Near NYC) was very cheap both for rents and real estate prices, compared to Manhattan. But when news of a new bridge came out to replace or compliment the existing ferry, prices and rents went up drastically. Same where a new underground or railroad stop will make a place more convenient.
Prices/rents in coastal North France went up with the Channel Tunnel making that area more accessible to London commuters. The trick is to get in early. Move quickly.
Just a few years ago, I recommended Panama City and suburbs because Panama had just contracted for a multi-billion expansion of the Panama Canal and other public works. A new visa program was instituted to encourage 100,000+ new technicians and needed workers to come to Panama. It was obvious that many condo rentals would be needed.
A few of my consulting clients and friends took my advice. They picked up or built good high end condo properties. They were able to get 14% net returns on rents and another 20% a year on appreciation. With 10% down deals, that means tripling their money every year. The Panama boom is coming to an end now that the work is nearly complete. I see a plateau rather than a bust coming to Panama. But in my opinion the best opportunities have come and gone.