Type a coefficient in front of each formula. The atom count on both sides updates as you type, so you can see straight away which element is still short.
Reading the chart. Each element gets a pair of bars. The dark bar is the left side and the teal bar is the right side. When every pair matches, the equation is balanced.
Two habits that help. Start with an element that sits in only one formula on each side. Save oxygen for last, because it usually turns up in several formulas at once.