Not really high. I am a natural night owl but I was working at a job that had a more traditional 9-5 schedule, so I was taking them about 1.5mg about once or twice a week, just to help regulate my chaotic sleeping pattern. I used to buy 3mg pills and cut them in half. If I went for a long time without taking it, or if I took a whole pill instead of half it would be almost guaranteed that I would have lucid dreams.
How do you increase your melatonin?
By taking an higher dosage of whatever they're taking for sleeping.
You might be mistaking melatonin for melanin (the skin colour one).