Garam Masala is the Indian equivalent of French herbes de Provence or Chinese five-spice powder.
The recipe changes from region to region within northern India, make it the way you like.
The flavors will be much stronger is fresh spices are used.
Rosebuds (found in Indian or Middle Eastern markets) can add an exciting floral note, you can use black cardamom, or fennel seeds . Once you taste the difference that this simple powder makes in your cooking, you will find it worth the investment of cupboard space.
As a rule (one that certainly gets broken all the time):
Garam Masala is only added at the last step of cooking, almost like a fresh herb, because it tends to become bitter if cooked too long.