Resource management is the core of Banished. Food, firewood, and tools are constantly consumed. Always aim for a surplus, especially before winter. Monitor your food production versus consumption in the 'Information' tab. If production is low, build more food-producing structures or assign more workers. Firewood is equally vital; a shortage will lead to citizens freezing to death.
Population management involves balancing births, deaths, and immigration. Early on, focus on keeping your existing citizens alive and healthy. Avoid rapid expansion that outstrips your resource production. Children will eventually become adults and join the workforce, so plan for future labor needs. Don't over-assign workers to a single task if it leaves other critical jobs unattended.