Well, they all pretty much use normal CFOP for all of the layers except the top, and then for beginners (like me) they should use 4LLL, 4 look last layer. You can find all the algorithms here, in this link.
If you're going for world class, then you should use 2LLL, 2 look last layer.
There are a total of 329 algorithms to memorize, so I don't recomment to learn this unless you are very serious into megaminx.
Algorithms for OLL
www.speedcubedb.com
Algorithms for PLL
www.speedcubedb.com
For S2L (Second 2 Layer) the only thing you can work on to improve your speed is to look-ahead. Keep track of other pieces as you solve, so you can easily move on to the next pair.
I'm also a beginner at megaminx, but I've watched a few intermediate and advanced tutorials on cubeskills.com (made by Feliks Zemdegs) and they helped me a lot. Hope this helps.