Switch to draft rather than position control, and then adjust the top link length. It takes awhile to be good with a box blade and a lot of sitting sideways so you can watch the blade. For my new cab tractor I'm mounting a backup camera
DC Makes so you can move a full load without it digging more, and it allows you to scatter a load rather just drop it. A good starting point for top link is lower the BB and adjust the link so the box is level. Then depending on what you want do shorten the link will make it dig, It won't take much to start it digging. My DC has adj up and lower stops, lower is set dig until box gets full, up is set to scatter it.
A hydraulic toplink or taking the time to work the manual one is required to really make a box blade work. Tip the front up to smooth & deposit material. Drop the front without the sides digging in to much to cut more. I use my hydraulic toplink more than the 3pt lever when I'm grading. Letting the blade be more or less aggressive while leaving the 3pt all the way down eliminates a fair bit of the issues with the box blade raising or falling when the tractor goes over a bump.
Ripping ground up before you try to grade makes your life a lot easier. Especially if you have a lighter blade.
Filling in low spots often doesnt help. The loose dirt or gravel you put in divots ends up popping out. Generally you need to rip up the area around the divot as well as the divot itself. Then level things & pack it all down.