First Samuel tells the story of the transition in Israel from the period of the judges, to the time of the kings. It had been God's desire to rule over His people in a theocratic from of government, but the people of Israel saw how other nations were governed and wanted a human king to rule over them. To their own detriment, they insisted on having one despite God's warnings to the contrary.
In this book we will see that God gave them over to their desires, and gave them a king - Saul. Saul had all the potential to be a great leader. He was tall, good looking, and a very charismatic person. But he had a weakness (as all men do), pride. Therefore, he did what was right in his own eyes, and did not obey God and follow Him. His story serves as an example of what happens when human leaders don't follow God. His reign ended in a dismal failure. Sound familiar?
1 Samuel also chronicles the rise of David, Israel's second king. He was a man after God's own heart, and God used him mightily, even though he wasn't sinless. And, it would be through through David's lineage that the Messiah would come, the ultimate King of Israel.
This book has many great stories ahead for us to learn from. The most important of which is, how a successful leader seeks leadership from God.