Then Gracie will randomly show up in town. She doesn't show up every week, just randomly. She is kind of a rare visitor for many. Some have gone months without seeing her inbetween visits. But she will never appear on a Sunday and holidays. If you have the police station, they'll let you know when she is in town.
I have a bit of a recommendation for when Gracie DOES show up (which she will, like others said, after you've spent at least 70k at the T.I.Y.) in case you don't want to risk her appearing once every 39 years or so.
Basically, let's say Gracie shows up on August 4th. Talk to her, get your clothes to pass the fashion check (If you've been cataloging clothes then you should DEFINITELY just order some clothes from your catalog at a time before 5pm, then TT to like, 5:01PM and the clothes will be in the mail and ready), save and quit the game. Upon reloading the game, set the time to 5:59AM. Do not change the date, don't even touch the date. Just the time. Load up the game and wait 1 minute for the clock to hit 6pm, check the Plaza, and I'm pretty positive Gracie will be there.
I did this trick since I had the Emporium on my old town and figured "Hey, I earned it once, may as well give myself a break this time around" and it worked each and every time. Make sure to talk to your villagers though since this trick involves time traveling between days, meaning that a villager could potentially want to move out during this trick. It worked flawlessly for me and it's a lifesaver if you don't want to risk Gracie rarely showing up.
A bit off topic, I know, but in a way this DOES tell you how to get Gracie to show up more, no? Of course if you're against TT'ing then all of this is useless, whoops.