the minimum would be 100$ but you always go a little beyond that. It would be strange to finish a month exactly at 100$
You need to earn at least $100 for Google to send you a check. I advise you to go beyond $100, especially if you are living outside US wherein you might allowed $24 processing fee when they send to you your check.
There are not really any tricks... the key is: 1. Build a website with unique content that is useful for people 2. Build links into that content 3. Place adsense above the fold so people can see it without having to scroll 4. Continue adding regular content and building links into each new page The key is really no overdoing the linkbuilding... all you need is to keep getting regular links each week and gradually your site will move up the search results pages and get more organic traffic. The links should appear natural rather than getting 10,000 links one day and then none for 2 months.