My advice that I would give. First know what you are buying. Research and browse price listings.
I would say don't buy anything for at least a few months of searching... Some deals will pass you by, but that's fine, because you want your first pin to be the right one and not just any "DEAL".
Always play before you buy a machine if possible. There was a minor red flag when I bought my Breakshot. Not blaming anyone... Or if anyone gets the blame it would be me. The issue with my MPU board which is fried was slightly apparent when I first bought the machine, but I was too dumb to notice or know about it.
But, that also brings me to another point. I would recommend most people to buy a popular machine. That way you know there will be parts and that you can service it and replace it. A rare machine, by a rare company, the parts can be hard to find. But, even a special mech for a low selling machine can be hard to come by.
And this is my last bit of advice. Know your home, and know your pins replayability. Most people do not have a huge home. I bought a Hardbody and a Raven as I like the themes... But, the gameplay while fun, does not hold my interest past 10-30 minutes of gameplay. While I can play my Iron Maiden for hours on end. Yes... Iron Maiden is newer. But, I think you should always try to buy deep games for home use. If you can have a 4-5 pin collection, then all means get a few more shallow games. Something like a Sorcerer or Space Shuttle I would consider a fun shooting, but shallow game.
Knowing what I know now, I wouldn't have bought a breakshot to be my first pin(and I love breakshot), I also would never have bought Hardbody or Raven and I enjoy both of those. I kind of wish I hadn't as I could have almost bought a Ghostbusters for what I paid for those. And it would take up less space in my house.
So really be mindful of your space.