First, let me say that different people enjoy different things. If someone enjoys the world they're in, even if it doesn't match up to the "standards" I'm about to post, it's a good world for them. But, in my experience, new owners can be turned off by several things. First and foremost is being overwhelmed and outmatched with a feeling of hopelessness.
Now, to answer your question.
1. Low turnover. If a world has 6-10 openings every season, there's a problem. One may not be able to identify exactly what it is but there is one. I won't call out any names but, when I left a world reasonably recently, someone asked me about it. I said "The world seems to be moving in the right direction but there's something about it. I can't quite put my finger on it but I expect they'll struggle to fill soon enough and return to their previous status." They did.
2. Level playing field. Everyone can't win 75-85 games. But, if a world is full of 100 game winners, 100 game losers and very little in the middle, there's a problem. The balance has gotten out of hand in a game designed to be balanced. It's a situation, depending on how bad it is, that could take real life years to resolve. N00bs don't need to take part in those worlds. The game is hard enough on your first day. No need to make it harder.
3. A good personality fit. There are good owners and good worlds that don't match up. Some worlds are, by nature, a bit argumentative. If a lively chat where people don't mind airing their disagreements bothers you(and you're unable to figure out the block feature), you don't need to be there. Same goes for the quiet worlds. If the only post, every other day, is one owner complaining about injuries, seems too quiet for you, you need to seek greener, louder pastures.
4. A world that screens their owners to make sure the new guy fits. Some worlds just want warm bodies. You say "I'll take a team" and you have the password in 12 seconds. They don't care if you stay or go, they just want to play. A good world wants owners to be around for years.
The key is to find something that suits you. Taking the first available team so you can "play now" is a bad choice. You're stuck there for 90 days. And, since this is a dynasty game, you need to plan to be there for awhile. If you're just interested in "getting your feet wet", learning and moving on, I'd suggest a public world. While the public worlders hate me for saying this, there are no hard feelings with one and doners in public worlds. As a commish, I see one and done with skeptical eyes. But, if it's a public world, my view changes. Public worlds are open to the public. You get what you get.