On-page optimization is very important these days, there is no doubt to it, if you want to do on-page optimization then you have to learn it deeply for better result, I would say, no doubt to it.
Domain name business is really too profitable, there is no doubt to it, but you have to learn it first, if you don't learn it, you can't earn good money.
This is the time when you need to build natural links, there is no doubt to it really... you can use almost all the methods of link building to build natural links, I would say.
Well, writing quality content would always help a lot, there is no doubt to it, what you need to do is to write with quality and maintain keyword density too, it helps.
