Your best gravy secrets

I make sausage gravy as previously described, flour into the cooked sausage and then your liquid after.

For a brown gravy in start with a roux. Mostly butter, or olive oil if anyone is dairy allergic. Cook until dark brown then I'll toss another spoon of flour in and cook for just a bit more. The darker a roux, the less thickening power it has.
Next I'll add onion powder. It browns readily and quickly and so once it gets aromatic I add my liquid. It helps if that liquid is already hot or warm, but so long as you have a whisk and get it simmering I've never had clumps either way.
I rarely use water for anything. So either stock, cream, drippings, or another sauce goes in and let it simmer while stirring constantly over low heat - anything thick will burn if you rush.
Seasonings are to taste. For beef I go heavy and will use red wine, balsamic, or even a couple dark beers. I'll often make a reduction of dark beer (starting with some tomato paste in the pan that I hest to roast a bit before adding liquid) and then add some marmite to it along with pepper, anise, cardamom, nutmeg and plenty of chili powder. Once that's reduced by at least half it goes into the roux. Aromatics like roasted garlic, coriander, and sometimes basil goes last to keep the flavors there. It can be strained before putting into a gravy dish, or just leave it all together and enjoy the rustic result.

Lighter and white gravies I like to thicken with cornstarch or gelatin. Flour still works, but I always cook it at least a minute or two in oil or butter before any moisture gets added to avoid a "raw flour" taste. If it's not the sausage gravy, then I like to add gelatin which helps dryer white meats feel juicier when the gravy is added. Works a treat with turkey. I again use lots of onion powder as to me it helps the taste without loading up on salt and makes a small amount of salt go much farther. Celery, scallion, garlic or garlic scapes are also good additions to help add depth.