Breast are hard to make juicy because they have so little fat. We prefer thighs.
There was a lot of good advice on the steaks. But for time saving, hit it with a mechanical tenderizer and get the grill super hot. We like ours rare, so just a couple of minutes on each side, depending on thickness.
I marinate my chicken breasts in Paul Newman's Italian dressing for a day in the fridge then cook it using avocado oil and I sprinkle a little bit of cayenne pepper when the breasts are nearly finished cooking.
The best method I've found for cooking chicken breasts is on a hot cast iron skillet. It allows you to sear the meat on both sides which gives you a nice brown crust on the outside while the inside stays very tender and juicy.
Now with that said, you've got to buy high-quality chicken in the first place. Some chicken is just junk to start with. If you're buying wal-mart chicken in bulk or something like that, you may not end up with a good result no matter what cooking method you use.
For chicken, I set my convection oven (a big, regular-sized oven, not an 'air-fryer') to 425, put the seasoned breasts on a slotted rack with drip-pan, and give them a light spray with canola or coconut spray oil. I put them in for 17 min., then start using a good meat thermometer to get them to 160F. Always nice and juicy when done.
Steaks are harder for me but preheat a cast iron skillet for 15 min in a 500F oven and sear stove top 2 min each side. Pop back in the oven for another 2 min and rest on a plate for at least 5 min. I always use the thickest stakes I can, thin ones are too hard to get to rare- or med-rare temp.