What is he worried about? Is it too hard for him? Is he forgetting what he needs to do or when it needs to be done? If you're more specific, people can help.
With my son, we had all these issues. He was constantly disorganised, getting stressed because it was too hard, etc. After a couple of weeks of one disaster after another, we took over. We managed him in terms of telling him what to do and when. We also virtually did his homework for him, dictated answers, read the text books with him and googled with him, sat and revised for tests with him. Yes, I know you're not supposed to do that, but for us it was the only way to avoid meltdowns and him still being up at midnight doing homework he'd forgotten about!
Over time, we eased off as he got into good habits. First the management part, as we withdrew and let him make his own decisions about what needed doing and when. Then for some subjects which he was doing well in, we let him do it fully himself. Other problematic subjects still needed our input. At the end of year 7, we did a revision timetable for him for his end of year tests and he followed it and did well.
At the start of year 8, we "hovered" over his homework for a few weeks just to make sure he carried on from where he left off, but soon could leave him to it. Now he's in year 10 and he's fully independent and controls his own schedule. We still need to prod him occasionally to actually turn off the IPAD/Xbox and get on with it, but we certainly don't need to manage what he does or when he does it.
For him (and us), micro-management at first, with us pulling back steadily over the first year worked very well and the good habits he learned have stayed with him.