Ukulele Core Skills addresses all the practicalities (tuning, holding the uke, attaching a strap, changing strings) as well as the musicalities - playing chords, strumming, playing notes, learning songs.
It is written for beginners and players who have some skills but still aren't sure about a few things or would like to improve their ukeing.
Each chapter in this PDF eBook covers a different skill area, commonly encountered challenges and proven ways of dealing with them. There are tips throughout, 5 minute exercises for playing skills and links to demonstration videos and other resources. At $5.50, it's a dead set bargain!