Scales are always a good thing to practice.
Practicing your scales helps you find your way around your instrument.
Just like childhood melodies a major scale is something you can probably sing in tune, practicing the different major scales will help to improve your intonation.
Listen to yourself when you play the scales, try to be aware of the sounds you produce. This can be difficult when you are just starting out and are still trying to find the right notes.
Don't try to play fast, but try to play the scale well.
Pay atention to the transitions between the notes, the length of each note and the tone.
When playing a note short and with power, try to play with a constant position of the tongue and lips.
Make sure the power needed for the short attack is generated from the diaphragm and not from motion in the tongue.
Practice this by first playing a slow controlled note, concentrating on the position of the tongue. Stop the airflow without changing the shape of the mouth and the play the note by producing short bursts of air from the diphragm.
While doing this try to think of projecting your breath trough the harp.
A good way to practice to relax the facial muscles when playing an overblow is practicing a very slow vibrato.
Gently play the overblow and start a slow wide vibrato. While playing the vibrato concentrate on the muscles in your cheeks and lips.
These should be relaxed since they are not needed for playing the overblow nor for producing the vibrato.
Example Eb slow vibrato