Basically, in other words, if Kirby is on the ground, never go right above Kirby (or you will be hit by up-tilt). If Kirby is in the air, never go below Kirby (or you'll get hit by Dair... and don't even think of shielding it). So basically, always stay to the left or right of Kirby, and never go in the same vertical line as Kirby (unless Kirby's in the air and you're above Kirby... that's the only safe spot in the same vertical line as Kirby).
Try to hit him with the tip of your attacks (i.e. the fingers of his back-air, the toe of his forward-air/up-air). Never run into Kirby for a grab unless you hit him with something first, and you have enough time to grab him. Otherwise, he will up-tilt you, and as MATTS said, "if you get caught in the "FOOT" (up-tilt)you lost".
Also, learn how to smash DI. I have actually successfully smash DI'd out of Kirby's up tilt several times before (on the 64 controller, on console). If you can do that, you will reduce the amount of up-tilts that Kirby can do on you... which may save your stock (though you will still have high damage).