To give a talk (or more generally, to do a thing), loop through these four steps: establish your intent, develop a plan, practice, and learn. For a research talk, your intent might be to convey a single idea you need to choose, so your plan would be a tree whose node hierarchy and edge traversal you need to optimize and declare. Whereas your practice might follow a script, the memory and feedback you get would help you engage your audience and execute your intent in the present. Above all, a talk is an episode of cooperation with other people! So be honest, stand up straight, and breathe.