Apart from the obvious ones of like, getting a visa and difficulty of getting a passport, in rough order of my completely non-scientific guesstimate

• Stability, safety
• Long-term track record of employment opportunities, and pay vs cost of living. You want to be able to find a job, and not starve.
• Price and quality of government services such as healthcare, education etc.
• Language situation. As an English speaker, you’d either want to go for English speaking, or somewhere where people speak alright English but let practice their language so that you can eventually learn it. Also, see language difficulty for English speakers
• Culture and attitudes towards immigration; how difficult is it to socially integrate
• Matters of taste, would you like the culture, food, climate etc.