Look for context clues that indicate probability or reliability, like 'reliable' or 'likely to succeed'. Going with Emma's plan is a safe bet since she's thoroughly researched her facts.
Pro Tip 2/3
Avoiding Risk
'A safe bet' often implies a low-risk option in contrast to others that are more uncertain. With cloudy skies, bringing an umbrella is a safe bet.
Pro Tip 3/3
Colloquial Use
This phrase is informal, more common in spoken English or casual writing, not in formal texts. If you're hungry, Joe's diner is a safe bet for good food.