>>552304What helps me is using my phone's built-in functions to crop any unnecessary bits, and then resize the image (I prefer to keep the highest dimension under 1000px), and save the edits as a new file. This is the minimum, but I also do things like lower the saturation, increase contrast, and alter brightness to make it look a little bit better.
If your default image-viewer has an Edit function, explore its features, and most importantly make sure you know where your saved image is going so you can find it easier.
I'm using a relatively old model of Samsung, and I know every phone is different, but I hope I was of some help.
