Set the deck height to whatever you cut your grass at.
Adjust tire pressures. Ideally you want the two rear tires to be equal, and the two fronts to be equal. Side to side is what you're after, not so much front to rear. Typically on the BX's, about 22 in the fronts and about 15 in the rears seems to work.
Measure your cutting height at the blades. Lots of cources say to measure at the deck shell and that's dead wrong. The deck shell doesn't cut the grass. Turn the blades so that the left and right blade are pointing to the left and right, both about equally. Measure, then adjust side to side as needed. Within 1/8" is fine, I like them to be zero from side to side but I'm picky. 1/8" difference is not noticeable when cutting.
Now turn the center and right blade so that they're facing fore and aft. Measure the back side of the right side blade, log that measurement, and then measure the FRONT side of the center blade. You want the front to be about 1/8" lower than the rear. The reason the front needs to be low is so that as the mower is traveling forwards, the front 1/3 of the blade is doing the work. This takes some load off of the deck drive and also frees up a little horsepower. I have successfully run them at zero bias front to rear and it cuts better, slightly, but it also takes more power to do it. Typically I won't set a mower at zero F-R bias unless it's something that's got plenty of power; like a BX2670 or a ZD331 with a 60", something like that. Or if I know a consumer is either mulching or extremely picky. Mulching is a whole different ballgame.
Cutting tips. Mow in different directions each mowing cycle. If you're mowing, say, a 1 acre yard that is open, one mowing you can cut it in circles. The next mowing cut it diagonally. Next time cross ways. So on and so forth. So many folks mow the same direction all the time and it will affect cut quality. Keep the blades sharp. Rounded tips will negatively affect your cut, and drastically even with a LITTLE rounding on the corners of the cutting edges. It doesn't take much to make a big difference. Blades wear out. If they're rounded, replace, don't sharpen. If the ramps are worn, replace. I see them in the shop constantly, the ramps wear right where the ramp meets the main part of the blade, and eventually if you don't watch them, they'll begin to crack. A crack will run down the length of the blade, then the cracked part falls off and goes through the rib cage of somebody's kid. Mowers are dangerous machines.
Mulching. You need to slow the travel speed down. You can't cut as much off the top of the grass. You can't mulch wet grass, not at all. Deck must be level front to rear and side to side, within about 1/8" max. And the blades should be sharp. I've found on our old fleet of ZG222's that a razor sharp edge mulches MUCH better than a "typical" edge. I used to grind the edges on brand new blades if that tells you anything. But a sharp edge like that also is susceptible to getting dinged easily, so the operator has to be mindful of what he's mowing over. On my G1900/54" I will mow everything that's under 3" in diameter but my yard is not a manicured yard, thus I don't put a lot of attention into blade/cut quality. Probably better than most of the neighbor's yards but I don't go out of my way. There is no way I'd do it with another brand mower, no way at all. I used to sell John Deere stuff and 99% of them would be back at some point with a bent deck shell. That is, until they came out with the old 7-iron decks which were about 1/4" thick steel. They didn't bend easily.
What's your mower doing? If you see 3 stripes behind you, the deck is not level front to rear. If you see a "stepped cut", it is not level side-to-side. Balls of clippings, going too fast or the grass is too wet. Uncut wire grass? Going to fast and/or taking too much off.
There's a few thoughts on mowers, for what they're worth; and all are assuming that the mower itself is in good mechanical condition. Worn spindle bearings will affect the cut. Worn idlers will let the belt slip, affects the blade speed and cut quality. Etc etc.