'Everything begins with an idea.' - Earl Nightingale.
It's so true that it makes it absolutely agonising to have projects lined up and not a single idea to your name. The freedom of choice is lovely, except when you're trapped indoors by the limitations of your own mind. You try and try to think of something, scribbling down scraps of thought and random words as they bounce through your brain, but none of them seem good enough to grow into a truly good concept.
So, what makes a good idea? When I think about that question, the first thing that comes to mind is need. If nobody wants your idea, what use is it? Simply thinking about the holes in whatever industry/market you're working in can allow you to come up with ideas you wouldn't have by just thinking about your own preferences. Even asking others what sort of projects they'd like to see/buy/read/consume can lead you to stumbling upon an untapped treasure trove of inspiration.
Of course, once you've found something, you have to make sure you can actually pull it off. I've had some amazing (in my humble opinion, of course) game ideas that were magnificent on paper, but was I really going to be able to pull off a complex RPG adventure with a rich, detailed world and a unique range of NPCs in 3 months? Probably not. Luckily, we don't necessarily have to completely scrap our skyscraper high ideas. With a bit of brainstorming, and filing down, a gigantic good idea can become a reasonable good idea - a short RPG adventure with several interesting NPCs, and hints at a complex world without the need to build it completely: now that's doable.
Aside from finding the idea, making sure it's useful, and of course knowing that it's workable, a huge chunk of the success of a good idea is being passionate about it. Love your work, and of course, it will feel a lot less like work as a result. If you don't love your idea, see if there's a way to make it lovable. Change the theme, or the software, or the story, or the colour scheme - whatever it takes to make it worth your while. An idea can't be good unless you believe yourself that it's good.
'But the truth is, it's not the idea, it's never the idea, it's always what you do with it.' - Neil Gaiman.