Picking a good market might be the biggest thing. If you pick a market you don't understand, it's way harder to build a good product that solves an important problem well. You end up guessing a lot. It's also way harder to get the word out, because you don't know your customers well enough to know where they hang out. If you go to https://IndieHackers.com, sort by revenue, and pick the companies making the least, the most common phrase is some variation of, "I haven't really done much marketing yet," and it's often because they're in a market they don't understand well.
I'm also a big believer in automation. I haven't done nearly enough of it, but I just got into using Buffer for Twitter, and it's a tremendous time saver (I can do all my tweeting for a week in a single 2 hour block of time). I have a ton of other marketing tasks that I could automate as well. Also, Mike Carson of park.io is making like $1.5M/yr as a solo founder/employee, and he claims it's mostly due to automation, so that's kind of hard to ignore :)
First off, if no one wants to talk to you about your idea at all, then it's probably a bad idea. I know this one is fairly obvious but I missed it a number of times. It's important to make sure you always are trying to get customers or users. If you can't get anyone at all then you're basically not making something anyone cares about. Psychologically you may say to yourself "if I only add another feature people will listen". Life is short. They probably won't. Try another idea.
Second, if people will talk to you but won't buy your product until you add a new feature, and everyone has a different new feature, you have a product no one wants. I have tried so many times to just add the next feature that will make everything sell. It has never worked for me. I should have just stopped and found a new idea.
Third, you have a product that you don't want to sell. I know, this one sounds silly but I have had amazing product ideas but I couldn't drive myself to want to talk about it with anyone. Maybe I made myself feel better by making a landing page and crying about no one buying it every though "I was doing everything I could". But, it wasn't everything I could do. This one is a funny one because I might have been able to sell the product, I just couldn't bring myself to get up and do it. If that's the case, you have the wrong product idea FOR YOU. Stop, think of another idea, and move on.
Those are my biggest three categories right now. It all comes down to selling the product. If you can't sell it, then it's not something to work on. With my current product I love talking to customers and potential customers. I am excited and the sales line up with that excitement. They are excited to use the product. They enjoy the product and while there have been feature requests they are either a) after the sale is complete and I have money in my pocket or b) the same requests from every customer so I can tell it's a market need and not just a customer want.