How can I be less 'intimidating' to girls?

I've talked to some of the girls I'm sort of friends with and others I passively know from the clubs I run, and a lot of them have openly told me that I'm 'intimidating' to them (or was intimidating when they didn't know me well). I'm not quite sure why this is happening. Going forward, I don't want this to be an issue when starting relationships, so if any of you could provide some insight into what girls might find intimidating, I would greatly appreciate it. If you need to ask me any questions to support your answer, don't hesitate.