Think Playdoh consistency. Just like bread dough, if it's too wet, add more flour, if it's too dry/dusty add a splash more water. The keys that I've found are to make sure you've mix them thoroughly (no lumps) and to give the flour time to absorb the water before piping it out onto the lid. Just a couple of minutes seems to do the trick. Just another one of those things that comes with a bit of practice.