If you want to get into the angel game in 2017, and you want to do it to make money, then I'd sincerely advise you to go take out $5-10k for a weekend in Vegas, and try to get really good at a game of complete chance, like roulette.
"Good" at roulette, you're thinking? What can that possibly mean?
It means having a large bankroll and knowing your tolerance for burning through it. It means understanding how to pace yourself, so that you're not blowing through your bankroll in the span of a few minutes. It means getting the itch out of your system, if, indeed, this is merely an itch.
Can't afford to fly to Vegas and blow 10 grand in a weekend? Don't get into angel investing. You can't afford it. I say this not as a snobby rich asshole, but rather, as the sort of nouveau-riche asshole who lost quite a bit of money many years back, doing exactly what the author did, and losing money I learned in retrospect I didn't really want to lose.
I still make the occasional investment, but as part of a group. By and large, those investments go to founders we've worked with before, or who come highly regarded. We invest super early, we eat a fuckton of risk, and we expect to lose 99.999% of the time. We're too small-time to play the game any other way at the moment.
Angel investing is about bankroll and access, and if you're wondering whether you've got the right access, you don't. So you're left with bankroll. Have fun, and try to get lucky if you can help it. :)