Tangier Med vs Tangier Port. This is the single thing that catches people out. Algeciras ferries dock at Tangier Med, a purpose-built cargo and passenger terminal 40 km east of the city. You cannot walk to anywhere useful from there. Budget 60–90 MAD for a grand taxi to the medina, or pre-arrange a transfer. The Tarifa ferry, by contrast, docks at Tangier’s old port, a short walk from the Grand Socco and the medina entrance.
Border paperwork. Fill in the entry card on the boat; they are handed out by crew. On the Moroccan side, keep your entry slip — you will hand it back on departure. Spanish residents who are non-EU nationals should carry both their passport and residencia.
Guides and touts in Tangier. Tangier has improved dramatically since the 2010s but unsolicited "guides" at the port and medina entrances are still common. A genuine licensed guide works with a badge from the Ministry of Tourism. For a short trip, booking a private half-day city tour through a reputable operator before you arrive is the most efficient use of limited time — and cuts through the noise immediately.
Money. Withdraw dirhams from an ATM at or near the port rather than exchanging euros with street vendors. Bank ATMs at Tangier port (Attijariwafa, CIH, Banque Populaire) give a fair rate. The dirham is a controlled currency — you cannot buy it in Spain before you travel. Expect to haggle in souks; first prices are rarely final.