Mozart's Adagio in E major (K.261) is a standalone movement, likely intended as an alternative for a concerto, characterized by its flowing melody and elegant harmonic language. It's a staple for developing a refined classical style.
Emphasize clear articulation, graceful phrasing, and precise ornamentation.
Adagio in E major (K.261) is rated Henle level 4 of 9 — intermediate repertoire, roughly ABRSM grades 5–6. In the RCM system it corresponds to about level 7.
You should be comfortable at Henle level 4 — meaning you can already play level 3–4 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 Adagio in E major (K.261) lasts about 6 minutes.
Adagio in E major (K.261) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.