Carom (Ajwain seeds) have a similar flavour as thyme. In a pinch, thyme can be used in its place. If you use cardamom pods, you just have to break them open and grind the smell seeds inside. Mustard seeds, fennel seeds and cumin seeds need not be ground. However, for optimal flavour, make sure to toast the spices. Cinnamon sticks should be removed from your dish before serving.
Garam Masala is a blend of ground spices common in North Indian cuisine. It is a blend of spices that varies from family-to-family and region-to-region. Spices are toasted and ground together. A typical Garam Masala contains black + white peppercorns, cloves, cinnamon, cumin seeds and black + green cardamom pods. Garlic and ginger may be added as well. According to Wikipedia, the key to a good Garam Masala is balance, so that not one spice overpowers the entire mixture.
Note: I find spices stay fresh for up to 6 months in a dark, dry cupboard.