I love to use actors to represent my characters. I picture my hero and heroine in my mind then scroll through photos of people I think might “look like” my characters. Then when I write a description of that character, I have a visual representation.
What’s strange is I know my character well before I go through the pictures. As I scroll, I say no, nope, not her, couldn’t be him, but then all of a sudden a picture will pop up, and I know for a fact that’s my character. Like Janie Littleton and Luke Chamberlain, the heroine and hero of Restoration of the Heart. 
Luke Chamberlain and Janie Littleton
The villains’ pictures stand out as well and usually say “Choose me.”
Mildred and Hector Hawker