After you ride through Route 15 with Sharpedo, you can explore Route 16 and Ula'ula Meadow.
Explore Route 16
In the Route 16 Pokémon Center, talk to the girl on the left. If you have used the Pokémon Cafés a lot, she will give you a Lemonade.
The girl on the left will ask you to catch Garchomp, then come back and show her your Pokédex.
If you approach the Café, you have to battle a Team Skull Grunt who has a level 35 Trubbish. You get 1120 Pokédollars for winning. Afterward, you get a Moomoo Milk.
East of the Pokémon Center, there is an Aether Foundation building, but you can't do anything there unless you catch Zygarde. Come back later if you catch one.
Outside, check on the right side of the Aether Foundation building to crawl behind it. You will battle Preschooler Kindra. She has a level 34 Mimikyu. You get 408 Pokédollars for winning.
Go south from there to get TM81 X-Scissor. Then go up and check on the north end of the building to crawl back through.
Go southeast from here to find a PP Up.
In the grass, you can battle Scientist Reid. He has a level 35 Charjabug and a level 35 Alolan Muk. You get 1680 Pokédollars for winning.
After this, you can go north from the Pokémon Center to reach Ula'ula Meadow.
Go north along the wooden bridge. There will be a cutscene.
Keep going north. There is a Poké Finder spot to the right.
Up ahead, there are some stairs down to the flowers. There, you can battle Dancer Mireille. She has a level 36 Floette. You get 1440 Pokédollars for winning.
To the right of the Dancer, there is a Repeat Ball.
Go back up onto the wooden bridge. To the east, you can battle Office Worker Michelle. She has a level 36 Torkoal and a level 36 Whimsicott. You get 1440 Pokédollars for winning.
Go northwest, to where you can battle Lass Rylee. She has a level 35 Sneasel and a level 35 Komala. You get 840 Pokédollars for winning.
Go to west from Rylee, and go through the grass at the end to get an X Sp. Def.
Go back to the wooden bridge, and go north, then down the stairs. Go to the left to find an Adrenaline Orb.
Go back onto the bridge and go north. At the end of the bridge, you can battle Actor Meredith if you have battled her in previous locations. She has a level 36 Baile Style Oricorio. You get 1440 Pokédollars for winning.
Go east from Meredith and go through a patch of grass. Keep going east to find Lake of the Sunne/Moone. Go north into the ruins. In the upper-right corner, you find TM03 Psyshock. There is nothing else to do here, but you can keep going north if you want to see the rest of the ruins.
Back in Ula'ula Meadow, if you have defeated all of the trainers there, you can go back to the south end of the meadow and talk to the golfer to battle Golfer Dean. He has a level 39 Hariyama and a level 39 Alakazam. You get 2340 Pokédollars for winning. Afterward, Dean gives you a Flame Orb.
Go north over the bridge and keep going north to reach Route 17.