Get a good instant read thermometer. If you want one that is Bluetooth compatible and wireless, the temp spike is the one to go with. I have the dual one with two probes.

Start with pork butt. Is by far the easiest to cook and difficult to mess up. You just need to get a good recipe for the rub. I found a famous Dave's rub recipe that I use for pork butt and ribs.

I have found over the years that once I got really good at this, the right rub made all the difference in the world. I have several different kinds of rubs that I use for the different meats that I cook.

Buy bone in pork. You will get better flavor and the bone will actually help you determine when it's done. As it gets closer to 200° the bone will actually start to poke out of the pork. What I usually do is I grab onto the bone and kind of tug on it and if it feels like it's going to slide right out, you know the pork is done. Also, the bone pulls the meat together. Make sure you get a pork butt cut, which includes only a part of the shoulder blade. I have made the mistake by getting a shoulder roast which has this giant bone in it.

Don't cook to time, cooking to temperature. Use the time estimations to help you plan, but could do a temperature is the way to go.
For pork but I cook to 200° usually, although depending on the piece of meat it may take little longer or a little shorter. The bone test that I described above is the best determinant.

Baby back ribs are the next easiest, in my opinion. Costco has ribs that are good quality and the membrane that's on the rib side is already taken off so you don't have to do that. Look up recipes that use the 2-2-1 method. That's 2 hours smoking, 2 hours wrapped in foil, and 1 hour back on the smoker. The one thing about ribs is that they can dry out, so it's a good idea to put a pie tin full of water in the smoker. It helps with humidity and keeps the meat moist.

Chicken is also really easy, and doesn't take that long.

Brisket is the most difficult. Watch videos on how to properly trim it before you put it on the smoker. Cook a whole brisket, and not just a flat. The flat is super lean and honestly not my favorite. The point is much better because it has more fat marbling through it. I gotten pretty good with brisket But the prep on them is a lot of work.

I cook just about everything now on my pellet smoker. Even hamburgers and steaks.

Don't be afraid to use foil to wrap. Foil will help you especially when you are cooking pork and brisket, as they will get you past the stall. Foilers called the Texas crutch. Some people think it's cheating, but I don't think so and my stuff is almost always really good.