Here’s a handy little guide for those wanting to evolve their Pokemon in Sun and Moon…
Rattata evolves into (Alola) Raticate at level 20, at night.
Pikachu evolves into (Alola) Raichu with a Thunder Stone, which can be purchased on Akala Island.
Meowth evolves into (Alola) Persian with high happiness. Using a luxury ball to capture Meowth would immediately raise its happiness a bit. You can raise happiness by winning battles, giving it a massage in Konikoni city, and feeding it vitamins. You can check a monster’s happiness in Konikoni City, and giving your Meowth a Soothe Bell will increase how much Happiness it gains.
Graveler evolves into (Alola) Golem through trading, just like before.
Cubone evolves into (Alola) Marowak at level 28, during the night.
Exeggcute evolves into (Alola) Exeggutor with a Leaf Stone, which can be purchased on Akala Island.
Yungoos evolves into Gumshoos at level 20, during the day.
Rockruff will always evolve into Lycanroc, but the form depends on the game you’re playing. “Midday form” appears in Sun, and “Midnight form” appears in Moon.
Type: Null evolves into Silvally with high happiness. You can raise happiness by winning battles, giving it a massage in Konikoni city, and feeding it vitamins. You can check a monster’s happiness in Konikoni City, and giving your Type: Null a Soothe Bell will increase how much Happiness it gains.
Charjabug evolves into Vikavolt if leveled up while in Vast Poni Canyon.
Crawbrawler evolves into Crabominable if leveled while on top of Mount Lanakina.
Fomantis evolves into Lurantis at level 34, during the day.
Sandshrew evolves into (Alola) Sandslash with an Ice Stone, which can be obtained in Ula’ula Island’s Po Town.
Vulpix evolves into (Alola) Ninetails with an Ice Stone, which can be obtained in Ula’ula Island’s Po Town.
Salandit evolves into Salazzle at level 33, but only if female.
Steenee evolves into Tsareena if it knows the move “Stomp” (acquired at level 29.)
Some evolution items can also be obtained through Poke Pelago, where you can develop an island called Isle Aphun in order to find rare stones.
(via Kotaku)