Decide on the topic and outline major points and develop an idea for the thesis. This will narrow down ideas and also develop a larger perspective concerning the topic. For instance, if your topic is the importance of early childhood education, main points could be funding, available facilities and staffing. Brainstorm about these topics and you will have information for the top of the funnel.
Read over the brainstormed ideas. Choose one broad idea, like the end result or larger problem of your topic. Consider societal implications or monetary costs to interest your audience, but also to show readers that your smaller subject plays a role in a larger picture. In the example of childhood education, start with the difficulty of older children who did benefit from that experience. Write one or two sentences describing the expansive idea.
Review your notes and develop a thesis that addresses the main points of the essay. Now look at the broad beginning and the thesis; add information to connect them. Use transitions to connect each new idea. Show readers how the opening idea is the umbrella of your focused thesis. Work your way from the big picture to specific details that transition into the thesis.
Read each sentence separately once you finish the introductory paragraph. Rearrange sentences or ideas so that it reads like a funnel; information should start as a large flow but end in a trickle. Check that each sentence incrementally becomes more detailed. Review the finished introductory project with rested eyes so you can honestly evaluate the effectiveness of the funnel.