Identify who the main character(s) of your story is. This is your protagonist. You will not use their name in your logline, but rather a basic description of him. Examples include: "homeless man," "teenager" and "struggling artist."
Identify what this character is striving for. For example, what is their goal? What are they hoping to achieve during the story? There might be multiple things, but it's important that you identify the main goal. For example, in The Wizard of Oz, the main character's goal is to get back home to Kansas.
Identify what stands in the way of your main character achieving their goal. This is your antagonistic force. Like the protagonist, you will not identify this character by name, but rather a basic description.
Write your logline. Keep things in the present tense and use active voice. To show conflict, consider using a word such as "struggles," as this easily gets the notion across of a conflict. As well, be sure to keep your protagonist to the first half of your logline so it's clear that they are the protagonist. An example of a logline: "A young entrepreneur struggles to get his business off the ground when a greedy corporation moves into town." Another: "A well-known businessman struggles to regain his positive reputation after a competing businessman reveals his dark secret."