This is another early sonata movement by Mozart, likely written in his childhood. It embodies his early style with its clear melodic lines, simple harmonic progressions, and a generally cheerful disposition.
Focus on maintaining a light, detached touch and clear rhythmic precision.
Allegro (K.3) is rated Henle level 3 of 9 — late beginner repertoire, roughly ABRSM grades 4–5. In the RCM system it corresponds to about level 6.
You should be comfortable at Henle level 3 — meaning you can already play level 2–3 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 Allegro (K.3) lasts about 3 minutes.
Allegro (K.3) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.