It's not simple at all as it might seem to be. You need to be more clear about what tracks you want to include.
A 5-star song that played only once and a 1-star song played 100 times. Which song do you want to include?
How to set it up depends on that specific criterion.
For instance, you could add "rating over 4" rule, or "play count over 10" rule, or both.
Also you could create two playlists first that include a certain number of highest rated songs and most played songs, respectively, and then supply them as the source of the new playlist. Creating a playlist mixer is another option if you want to set a track count for each criterion.