You can also take opinions from friends, teachers, and elders to know the feedback and then research it thoroughly and practice

Speech is all about one’s own thoughts and what a student thinks of that particular topic in general. Do not copy the content from somewhere, try to understand and present it in your way by adding your opinions and personal touch.
School students are asked to speak on a topic so that they learn the art of expressing themselves in front of an audience and become good public speakers. 
Most schools ask students to choose the topics, some competitions allot topics beforehand and some are asked on the spot for speech. 
In case, you are asked to choose topics, then select an interesting trending topic or topic which requires the most of the attention but is ignored. 
You can also take opinions from friends, teachers, and elders to know the feedback and then research it thoroughly and practice.
Jolt down the structure to keep you on track. Note all points you want to convey and connect them properly and do not forget to keep it interesting.