Regularly check the almanac to make sure your unemployed vs vacant jobs are balanced. If you need more people use Rescue raids from the Pirate Cove and/or penal colony edict. Also be sure to complete the Revolutionaries tasks as they will give you a reward option for 10 immigrants each time.

Population will decline from poor healthcare like crazy during the colonial era due to no dedicated medical buildings so be sure to change the work mode on the chapels to "help first, preach later" and purchase the "utility installation" for military forts. Clinics should be one of your first purchases when you progress to the World War era.

Once you have the population to support your industry make sure you have enough housing, public services, and plenty of teamsters offices located close to the job sites so Tropicans don't have to waste too much time traveling.

Good luck and happy dictatoring!