As a Japanese person I find it pretty hilarious that "umami" is a trendy word in English now. So many chefs are lauding Japanese cooking techniques like it's a new thing. But guys, I have to tell ya, it's been around for centuries. You just took that long to catch up.
There are a bunch of "tricks" us Japanese have up our sleeves that totally amp the umami-level of a dish. They are super easy, super fast, with great results. In fact I feel like they are the best-kept secrets amongst the Japanese community.
Secret #1 - butter and soy sauce
Wondering what sauce to top your steak with tonight? Need an extra something for your veggies? Add butter and soy sauce!
Secret #2 - miso and mayonnaise (or any dairy)
Miso alone is powerful enough. When in doubt, add miso to your sauces/dressings/marinades. It adds depth, transforming an OK sauce to finger-licking good. The combination of miso and mayo is absolutely failsafe. Worried about making your chicken dry? Stir fry it real quick with some miso and mayo. Afraid of sawdust pork chops? Marinate it in some miso before pan-frying. Your friends will be begging for the recipe. Miso and butter work just as well.
Secret #3 - kombu (or kombu dashi)
If you don't really know what kombu is, you'll probably just say "wtf it's just a piece of seaweed." No, it is not just a piece of seaweed. It's the basis of the word umami itself. Monosodium glutamate, or MSG, is a man-made substance created to mimic the savory taste produced by kombu. As in yes, that piece of seaweed? It packs a punch of flavor.
Secret #4 - dried shiitake mushrooms (and the liquid from reconstituting it)
If you're vegan, all you need to make flavorful stock/broth with is kombu and dried shiitake. To reconstitute the shiitake mushrooms, stick them in a small pot with enough water to cover, bring it to a boil, then let it sit until the mushrooms have rehydrated. Add both the mushrooms and the liquid to your recipe.
This is definitely not the whole list. If I missed an obvious one, let me know in the comments!