Ask at the front desk about the fishing charters before you book anything online - the captains who run boats out of San Felipe have varying reputations and the hotel staff know which ones are currently working well, which ones have the best equipment for what you're after and approximately what a fair price looks like for the season you're visiting in. Sport fishing in the upper Sea of Cortez for corvina, sierra and the various other species that run through here is genuinely excellent and being pointed toward a reliable captain rather than the first boat that approaches you on the malecon makes a real difference to the outcome.
The tidal schedule matters more here than at almost any other beach destination in Mexico and it's worth looking it up before your first full day - the beach at low tide and the beach at high tide are such different physical experiences that planning around the tidal cycle is just sensible, not obsessive. Sunrise at low tide when the flats are exposed and reflecting the sky is a specific visual experience that people who've done it describe in terms that sound like they're exaggerating until you do it yourself.
Summer is genuinely difficult in San Felipe and that's worth stating plainly before anyone books July or August on the assumption that beach plus Mexico equals pleasant - temperatures above 40 degrees combined with the humidity coming off the shallow northern Cortez create conditions that locals manage through extensive shade use and midday inactivity and visitors sometimes don't adapt to quickly enough. October through April is the window when the climate is what most people imagining a Baja beach trip are actually imagining.
Bring more cash than you think you need because San Felipe's ATM situation is limited and card acceptance is inconsistent at the smaller taco stands and market stalls where the best eating happens - the exchange rate at the Oxxo is not ideal but it's reliable, and running out of pesos in a small Baja fishing town on a Sunday afternoon creates a specific kind of inconvenience that's entirely avoidable with five minutes of planning the evening before.
The drive south from San Felipe toward Puertecitos along the coast is one of those Baja roads that isn't on most maps in the way it deserves to be - rough in places, slow, requiring attention, but following the Sea of Cortez through increasingly empty landscape with occasional fishing camps and beaches that have no names on any sign. You don't have to go all the way to Puertecitos. Just go south for an hour and pull over somewhere and sit next to the water and understand what this coast actually is when nobody's organised it for you.