"Sometimes I feel like there's something in an idea and so push it as far as I can but often struggle to get anything out of it. I feel like this can be quite a waste of time and want to know if you have any red flags that come up when you try something out that indicate you should stop the idea and move on to something else. I get tunnel-vision sometimes and my efforts could be better spent elsewhere."
This is really tricky, but I would say that these may help you:
If you are running out of steam, stop.
There’s no point banging your head against a brick wall. Move on, do something else and come back to it later with a fresh perspective.
When you come back you’ll either see the potential or you’ll wonder “What was I thinking?!” and ditch it.
Ask yourself: “Does this solve the problem the client is having?” or “Does this fulfill the client’s goals?"
If it doesn’t, then ditch it. To be highly sort after as a designer, you must first solve the client’s problems or help them achieve their goals (often the 2 overlap). It’s not about what you want for yourself. You want to betaken seriously as a professional? Then be the guy that people come to because they know you will get it done.
Go back to your research
If you have spent the time gathering information, going back to this will help spark new ideas. The client’s needs are your first priority (as mentioned above) so going back to the research with your new knowledge will be helpful as you may see something now, that you missed earlier.
The reason I stress going back to the client specific research is to solve client specific problems. You want work in your portfolio that solves client problems. Once you know what will achieve this, then you can make it look great. The next person who will want to hire you isn’t a fellow designer, it’s a person with a business that has problems.
Too many people design for themselves or their peers. This is why self initiated projects are either way too self indulgent or hard to pin down. There are no parameters or constraints to work within and therefore it’s not taken as seriously as a proper client job.
Do something else
Take the pressure off by doing something else. Another project or pursuit. The key is to give yourself some space and let your brain rest. We can only work in short bursts and need stimulation from other areas.
I hate to promote my own stuff, but have read of these and see if they help: