Movies like "Braveheart", "300" or even "Game of thrones" always show us two armies built up on two sides charging at each other. Were people really that less afraid to die that they'd just mindlessly storm ahead? What would the most realistic course of such battles look like?
This post provides a really good answer to your question by /u/Agrippa911:
https://www.reddit.com/r/AskHistorians/comments/1n29nz/what_typically_happened_before_the_start_of/