This charming piece by Tárrega is known for its delicate melodic line and subtly melancholic atmosphere. It's a quintessential example of his lyrical guitar writing, adapted for piano.
Achieving a truly cantabile (singing) tone and using rubato expressively are key to capturing the piece's wistful mood.
Adelita is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7. In the RCM system it corresponds to about level 7.
You should be comfortable at Henle level 5 — meaning you can already play level 4–5 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 Adelita lasts about 3.5 minutes.
Adelita is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.