Take the time to learn a few basic phrases in Spanish: hello, thank you, where is…, I don’t understand, please, etc.
Get the Baja Atlas and iOverlander. The Moon guide to Baja is useful, especially if you haven’t been to Mexico.
Get pesos before you cross, especially smaller bills, and plan on paying cash in pesos for almost everything.
Good advice above. San Felipe is close and easy because they are used to gringos and Highway 5 is better than many US roads. Travel in daylight and use common sense and you’ll be fine and probably discover that the people are largely amazingly generous and kind.