I feel like I have dealt with my ADHD fairly well until I overworked myself last year, so maybe some of my techniques could be helpful (for school stuff). I was never on any medication for it when I was younger (I also didn't know that anything was wrong with me), so I came up with my own weird solutions to make myself focus better:

1) The leg shaking was my first concentration technique. I shook my legs when I was having trouble focusing and wanted to pay attention. This helped provide a distraction to enable me to focus. It also kept me from falling asleep.

2) Music. I brought a CD player with me to school and hid it in my backpack. I kept my hair long so that I could hide the cord to the earphone. I kept the volume of the music at a level where I could enjoy listening to it while still being able to hear the teacher. Sometimes, I just used one earphone at a higher volume. (I was a secret rule breaker, lol)

3) Naps. I napped frequently after exerting a lot of energy. After napping, I usually felt recharged and ready to be focused again.

4) Exercise. I had a lot of problems with my emotions and screaming when younger. After I started exercising consistently, those problems went away. Anything aerobic is good for my mood.

5) Using a Daily Planner. This is what kept me on track. I couldn't remember anything unless I wrote it down in my planner. I had my entire schedule, all assignments, activities, and work times planned out. I lived out of that thing. I checked it multiple times during the day.

6) a watch. This helped me a lot for timed tests located in rooms without a visible clock. I like wearing a watch during tests because I can monitor my progress and determine when I get stuck in a repetitive thought loop.

I hope that these could be helpful. If you aren't already using a daily planner, I think that is the most helpful of the things I listed. It is difficult to get into the habit of using it, but once you do, it is really easy to stay on schedule and not lose track of time as much. If you already do all these things, sorry to repeat information.

On a side note, in the past when I had my life under control and was doing really well, if I couldn't focus at a time when I planned to get homework done, I would just indulge in doing something fun (no longer than one hour, though). I would then try to get back to what I needed to do after I did something fun. Exercise also helped me feel more focused back then.

I found this list when searching for answers after enduring a lot of stress last year. It is a list of tips for managing ADHD without medication (I too tried to get a psychiatrist to prescribe me medicine for ADHD a year ago, but he only wanted to give me antidepressants for depression, so I tried to help myself the best I could and this list helped me a little)
Adult ADHD: 50 Tips of Management « Dr Hallowell ADHD and mental and cognitive health

Reading this list of tips was actually what finally convinced me that I did indeed have ADHD.