Before I continue, I should probably put down a disclaimer about spices I use for my original recipes: I don't measure out my spices.
I know, I know, how terrible, right? I also almost never follow spice measurements from recipes when I'm cooking either (not when baking, though - I follow the recipe at least once when baking).
Most of a lifetime of lurking near a stove or taking up space in a kitchen has infused me with a pretty solid sense of what flavors mix well according to my tastes. That's the big caveat, I know what I like and I cook to that preference - a touch more salt (pink or sea salt), a dash of extra cayenne, a light hand with coriander, toasting cinnamon sticks before grinding, a cupboard full of cloves and cardamom and star anise.... Little preferences here and there that I've found work well with my casual culinary style. The other side of this is that I don't always have the spices I want or prefer for a recipe on hand, so I've become quite adept at experimenting until I find a another herb or spice that works well enough instead.
I highly encourage those with the budget or bravery to head to their local spice store, community grocer, or unexplored cultural marketplace (there's an Indian grocery not far from my house that I particularly like) and spend some time in the spice aisle. Look at what's available, look up anything that isn't familiar, pick one or two to try out. Start small and find highly rated recipes. Then move on from there.
I like buying whole spices when I can, and grinding them at home. While it's possible to toast pre-ground spices, I find it easier to toast whole spices then grind them. I put them on a baking sheet lined with parchment paper, pop them in the oven for a few minutes with the door just a touch ajar (the optimum temperature will depend the oven and humidity, but I usually start with 175*F). I don't toast every spice I plan on using. Generally speaking if it's green, I avoid toasting, if it's red or brown, it usually hits the heat before I grind it up and add to the cooking.
Endnote: I may turn this into a Page, but until then I plan on coming back and adding to this post with further suggestions, experimental recipes, new discoveries, etc. So check back periodically, as there is more to come!