Building Leverage with Suppliers Over Time

Hi everyone,
It seems like supplier relationships improve when there is consistent volume and reliability from the buyer side.
From a strategic standpoint, do you think leverage in supplier relationships is mainly built through volume, consistency, or negotiation skill?
Would appreciate insight into how others approach this.

Volume, consistency, payments on time, negotiation skills, geographical situation, competition within the same market, how you position yourself, how reliable is your brand/website, how structured is your business and the corp documents you can provided every time they ask you for something... everything is important.