You can choose a certain value to be selected by default on the dropdown and swatch options. All you need to do is check the selected checkbox on the value configuration.
To make an option selected by default
Browse to the option set, and the option within that set you want to edit (options with default values available are dropdowns and swatches). Click the desired option to expand it.
Scroll down to the values of that option
Expand the value you want to be selected by default
