You can set up default options on the "Settings" page.
For this go to the “Settings” tab, choose a default setting and click Save (at the bottom of the page).
On the settings page you can also connect product options with auto image swatches or global images (doesn't work for virtual products)
To do this go to the bottom of the "Settings" page and edit the settings for "Global Auto Images", and "Global Colors"
Just enter the names of the product options you want to be connected. For example "color, size, materials."
For colors, add the names (case and space sensitive) and edit the color for each.
Click "Save" in the bottom right.
For Global auto images make sure your variants are connected to images in the Shopify Variant System.