Well you've got to start somewhere. If you wait to find the perfect idea and perfect implementation you'll waste a lot of time and it may not work. Your first site probably won't make much money, but that's the beginning of your experience and hands-on education.
You can end up pouring most of your time into 1 website and be successful if you want, though I wouldn't recommend it. You need to diversify, to at least a couple sites, and a couple different revenue streams, with hopefully different traffic sources. This way if something goes belly up, you're still ok.
But you still have to find out what is going to work for you. You might get lucky on your first site - you wouldn't be the first person to do that, but it's pretty unlikely.
For example, say you build 10 sites on 10 different niches. Using different ideas and methods here and there to see what works for you. After 6 months, one of those ideas and/or niches is going to probably be considerably more successful than the others. You can focus there if you want or just keep it rolling and try 10 more.
In the process, you learn what works, what doesn't and how you like to run things. You apply this to all of your current and new sites. Then you continue to try new things and ideas and put your own twist on them.
You just need to get started.