If you are using public transportation from San Diego
Take the San Diego trolley to the Mexican border. After you walk across the bridge (that crosses the highway), go to the right and walk through the revolving gate. Continue straight ahead for a few hundred meters and take the first right turn that you see. Go through the revolving gate. Cross the street, turn left and continue walking up the sidewalk. After it turns to the right, you will see the bus station ahead. The bus line is called "ABC". Buses leave every hour to Ensenada.
If all you have is carry-on luggage, when you get on the bus, ask the driver to leave you off in El Sauzal at the traffic light (semaforo). If you don't speak Spanish, show him the following request, already written out in Spanish for you:
Sometimes the driver forgets and goes right on past El Sauzal. You can help him remember. There are 2 toll booths along the highway that he will have to stop at. When he stops at the 2nd one (about 1 hour and 15 minutes after departure) you are only 2 miles away from El Sauzal. If possible, remind him at that time.
Once you've been dropped in the vicinity of the PEMEX gas station, use this map to find the hostel.
You may want to print the map on the 'How to find us from downtown Ensenada' page as well, in case you arrive in Ensenada and need to find your way back to El Sauzal.