[Blarg]

Lots of good suggestions here. Some of the simplest ones are best.

Get a good sized spice rack, one with like 15 or 20 spices. Make it a goal to use each one within, say, a month, at least once. And to not give up if you can't figure out how to use the spice/herb perfectly the very first time. There are online resources that tell you how to use them, too.

And aside from pure flavor, there's always the spicy angle. I like hot sauce on rice a lot.

There was a time when I was almost 100% vegetarian that I made a simple sauce that wasn't ideally healthy, but everything else I did was so healthy I didn't sweat it. I would melt some butter in a small saucepan, being careful not to brown it, and then stir in some soy sauce and lots of black pepper and whatever kind of garlic I had on hand. (Warning against the powder: you have to use a lot to get a strong flavor, and adding that much can get you gassy. Fresh garlic is tastier and less gassy per unit or whatever of flavor.) This is a mix of a lot of strong flavors that you'll have to mix to your taste, but they work really well together. I have also substituted olive oil, to make it healthier. Not quite as flavorful, but still good.

Finally, frying and even caramelizing some onions is well worth it. And having some fresh chopped green onions really picks up the flavor and texture.

I'm also a big fan of what someone else suggested, sesame oil. A little goes a long way, and it is supposed to be extremely good for you.