This is a brief, charming Classical-era character piece reflective of the light song-accompaniment style of the early 19th century. Its clarity and simple harmonic structure are hallmark features of the period.
The student must maintain a steady Alberti-bass pattern while keeping the melody expressive.
Comparable difficulty and character — good candidates for what to learn next.
'Twas not those eyes of starry light is rated Henle level 2 of 9 — beginner repertoire, roughly ABRSM grades 2–3. In the RCM system it corresponds to about level 2.
You should be comfortable at Henle level 2 — meaning you can already play level 1–2 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
A typical performance of 'Twas not those eyes of starry light lasts about 2 minutes.
'Twas not those eyes of starry light is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.
Pieces at a comparable difficulty and character include 18 German Dances and Esoccaises by Franz Schubert, 18 German Dances and Esoccaises, by Franz Schubert, 18 German Dances and Ecossaises by Franz Schubert — see the full similar-pieces list on this page.