Lowering soil PH

does anyone have a favorite method for lowering PH? And are there specific methods I should stay away from?
Growing outside in pots.

I use a organic pine tree sap mix thanks to my lovely 4 story high girl in my yard but inside I use pH down by general hydroponics mixed in the water i give them and it gets the job done. Just verify information and if you ever hear of usinging coffee to water DONT just a tip my buddy found the hard way.