The airport is around 50km from downtown San Salvador.
Taxi - taxis are available on the Arrivals level. For a local experience, you can take a much cheaper, shared minibus (known as a colectivo) - but reports suggest these can get very busy and cramped.
Bus - local bus services run from the airport to central San Salvador and Comalapa. The bus stop is on the main road opposite the airport terminal, behind the parking lot.
Hotel shuttle - there's a courtesy shuttle to the nearby Quality Hotel Real Aeropuerto.
Car rental - you'll find a dozen or so car rental companies in the Arrivals hall. Exercise caution as a tourist driver - pedestrians will often walk across the roads without notice.