People are going to tell you what they do. But generally speaking, the top people in Texas all do roughly the same thing, outside of wrap or now wrap, and what form of wrap they do. Salt and pepper is mainly what people use. Some may use a garlic powder, some lawrys, some use some other stuff, but salt and pepper is 99% of it.

A flat kinda sucks to do alone, because it's notoriously harder to do right. People buy then because it's cheaper overall, but they don't realize the price per pound is dramatically higher. Costco or Sam's prime brisket is really hard to beat for the quality to price ratio.

But you have a flat, so that's what you've got now. You can smoke at different Temps and it will work just fine, but I'd prefer a lower temp (225) for the flat only. There's no think deckel fat to render out. Time will take care of intramuscular fat and the fat cap will get yellow and sticky with time and rest. I'd just throw it on the smoker with a water pan (help keep a little moisture in the cooking chamber) and after 1-2 hours spritz it with liquid. And no, the liquid really doesn't matter. But only try to spritz the meat, not the fat. You want the fat to render with heat, not cool it off. At around 170ish (use that term loosely because different smokers have different airflow, which creates bark) look at the bark and determine when you have enough color. When you do, wrap it tightly in butcher paper (tallow brushed on the paper helps) and back on the smoker. Or you can wrap it in a foil "boat" to keep the liquid in.

When it hits AROUND 195, start probing every 15-30 minutes for tenderness, NOT temp. People get this wrong all the time. Temp is only a loose metric for tenderness. I've had briskets finish at 195. Some at 210. Plus, thermometer accuracy also.

When it gets truly probe tender, which is zero resistance going in and coming out, pull it. Open the butcher paper/foil, and let it sit for 10-15 minutes until it's stopped rising in temp. Then wrap it back up, and rest as long as you can hold it over 140-150 degrees. Hours. This is arguably the most important part.