The photos I takes are carzy large and I always scale them down with paint.net. I prefer that over using an online service.
1. I open image with paint.net
2. I resize. Often I keep them 800px maximum. Often smaller
3. I export as jpeg and set the quality to around 60- 80%
Sometimes I also export as 8bit, 24bit etc etc instead of "auto" when exporting PNG. that reduces the size most.
for anything else (like my art files or decor graphics) I simply resize them with my drawing app. Scale down the pixels but so that it still looks good. Nothing fancy.