You have to be at least 35 years of age to be elected president of the United States. Therefore, a lot of people who serve as president have prior experience. The most common prior profession that presidents have before holding office is military experience. 32 prior presidents held military experience, with 9 of them serving as Generals in the United States Army. The biggest example of this is George Washington, who led the Continental Army to victory over the British in the American Revolution. Dwight Eisenhower also had experience commanding all Allied Forces in World War II before he was elected president of the United States. He also served as a general in World War 1.
There are also a lot of presidents who had careers as lawyers before they were elected president of the United States. The most recent example of this is Barack Obama. He enjoyed a successful, albeit brief, career as a lawyer before he ran for president of the United States and was elected for two terms. There are a lot of people who go into politics after a career in law. Just as it is very common for Representatives and Senators to work as lawyers before they join the government, it is also common for a lot of prior presidents of the United States to have careers as lawyers as well.
In addition to serving as lawyers, a lot of prior presidents also served as governors. There are a lot of presidents who have experience running a state before they step up and run the entire country. For example, Bill Clinton served as the governor of Arkansas before he was elected president of the United States. There are also plenty of other governors who have tried to run for president but were not ultimately elected to the office. It is important to note that many governors who successfully run for president generally govern a heavily populated state. In addition, Andrew Jackson served as a military governor, running Florida before it became a state. He eventually went on to be elected president, and he presided over one of the largest expansions in United States history.
Even though there are a handful of presidents who served as vice president, taking over when the incumbent president passed away (such as Harry Truman taking over for FD), it is also not unusual for someone serving as vice president to successfully run for re-election. For example, Joe Biden was vice president to Barack Obama before he was elected president. In addition, Richard Nixon also served as vice president before he was elected president himself. There are a lot of people who believe that serving as vice president is great training for someone who eventually desires to become president himself or herself.