Start with the source
If the PNG contains unnecessary pixel dimensions, resize it first. A 3000-pixel screenshot displayed at 1000 pixels does not need to keep all of those pixels.
Keep transparency when it matters
If the image needs a transparent background, keep PNG as the output format. Converting a transparent image to JPG will replace transparency with a solid background.
Use the right format for photographs
A camera photo saved as PNG can be unnecessarily large. If transparency is not needed, JPG or WebP may produce a much smaller file.
Use FormWise tools
The Image Resizer can reduce dimensions. The Image Converter can convert between JPG, PNG and WebP.
Check the result visually
Do not judge compression only by the percentage shown. Open the result at its intended display size and confirm that text, edges and transparency still look correct.