Nutmeg in mashed potato. Both tastes nice and gives an idea of the flavour.

Tumeric is not strongly flavoured, but using a lot in rice to make very yellow rice (add peas and fried onion) will reveal the flavour. Then, in a later batch add whole cardamon seeds, but don't eat the seeds themselves.

By coriander seed do you mean ground coriander, not whole seeds. If you know cumin already, try a mixture of 2 parts ground coriander and 1 part cumin in the same dishes you would use cumin.

Fenugreek - try experimenting with a very simple 'curry' spice mix made from fenugreek, cumin, coriander, tumeric, and chili powder. Start with 2:1 coriander and cumin and add other spices. Cook using frozen ginger garlic mix as well. And, consider adding tomato puree and creamed coconut. For amounts, start small and add more later.

EDIT: Try amchoor powder? It's dried and ground green mangoes. It adds a fruity sour flavour to food.