I’m a big believer in personal projects, and I’m usually running two or three at once, plus they never really finish to be honest
IMO, sometimes we can start off with an idea that’s a bit to open… this can be ok, as I think we tend to hone in on what we really want as we take more pictures and the concept evolves.
My ‘By the Sea’ series started off as ‘costal isolation’ but over time it changed what it was about. It kept isolation as a theme, but it became more an undercurrent, or put another way - I stopped looking for people looking miserable on the beach, and started looking for people engaged in an isolated way with their surroundings
If you set out too shoot say, (and I don’t mean to be deliberately facetious, it’s just easier to make my point) red cars or people wearing blue hats, then you’ll quickly know if you have a shot that fulfils your brief.
But if you set out to shoot things like happiness, joy or desperation, it can be a bit of creative quagmire as these subjects can be subjective
I’m not trying to dissuade you from pursing these example themes (and their ilk) but sometimes it’s better to aim for something quite specific, then understand the additional nuances and depth that these projects can bring - continuing my silly example, if set out to shoot people wearing blue hats, then you might end up with a series on happiness and joy (if it transpires that people wearing blue hats tend to look happy)
To pursue project ideas around emotion, I’d personally start by thinking about what the emotion looks like to you in a picture, then set about trying to capture it, then regularly review what you’ve got to see how it’s in keeping with the original concept.
Sorry to ramble on a bit…