Before you get started creating your site, it's worth taking some time to think about its design. This isn't just the visual design, but the user interface (UI) and components too. Think about the following:
Do you have an existing theme for your site that you want to use?
Is there a theme designed for BuddyPress (at https://wordpress.org/themes/tags/buddypress) that would work for your site?
What plugins are you already running on your site? Check whether they're compatible with BuddyPress; most well-written plugins should be, but any relating to membership or similar could cause a conflict.
What structure do you want your site to have? Will it include other elements that aren't part of BuddyPress, such as a blog ...