Hi two-sheds,
Interesting question! I suppose, if you have decent recipes (i.e. curry base and main dish) and have good "technique" (whatever that is, I'm still none too sure), then you shouldn't really have to add anything!
However, given that most of us (including me) lack one or the other, my list (for picking up taste, at least) would be as follows (in rough order):
- salt
- sugar
- garam masala
- curry powder/curry paste/spice mix
- fresh coriander
Some combination of the above should normally do it (unless you've really lost the plot!)
I suppose it depends on what you feel is lacking!