Most plants thrive and grow in soil in relatively neutral soil, but some plants actually prefer acidic soil: a pH below 7.0.

Example of plants that thrive in acidic soil:
Azalea
Rhododendrons
Hydrangeas
Blueberries
Cucumbers
Broccoli
Squash
You can buy pre-mixed acidic soil, but you can also acidify the soil you have. If you need to make your soil more acidic you can, for example add:
Powdered sulfur
Aluminum sulfate
Coffee grounds
Sphagnum peat moss
Nitrogen-based acidic fertilizer
To know how much you need to add, you’ll need to first pH test your soil. By testing the soil annually, you’ll also have a good chance to make adjustments before the soil’s pH gets too high.