Quiche is my go-to dish for using up leftovers. I flavour the egg and cream with vegetable stock powder rather than just salt.
When I'm feeling conscientious, I brush the base with some of the egg white to seal it a little to stop the filling soaking through and causing the dreaded "soggy bottom". But I always bake blind - shove it in the oven for at least 5-10 minutes while I'm preparing the filling.
It's a brilliant dish for a food processor. Mix the pastry, empty bowl, then chop the cheese, empty bowl and put on one side, chop any other things that can be done in the machine (spinach, bacon, etc). Then mix the egg and cream. All in the food processor without having to wash between steps.
Vegetables (e.g. courgettes, peas, spinach) can go in raw, but they don't give off as much taste as the cheese and ham or bacon. They need extra spicing!
Slices of tomato decoratively placed on the top before baking do, however, give an extra bit of oomph.
But even with just cheese, as long as you use plentiful amounts and a very strong-tasting cheese, the quiche should usually turn out tasty.
Keep trying.