New Game Plus

About New Game Plus (NG+)

In case you don't know anything about NG+, it's about playing the same story 2nd play through for the game. Usually the purpose of it is to explore other things you have missed out or additional NG+ events, probably applies for any games with NG+.

Why NG+?
Well,

• Unlock other Persona, such as Satanael. And I can bet most of you can't max ALL confidants' rank at first playthrough. In this case, you would have missed out some of the ultimate persona as well. 
• Additional boss battle: Twins Warden. You can fight Twins Warden anytime once you can enter Mementos. Talk to Caroline who stands beside the Velvet Room.

What carries forward in NG+?

Well, I bet you can easily get these information, but I will mention it clearly to make this whole thing complete.

• Money
• You social stat.
• Persona Compendium - Persona Compendium is just like Pokedex. For whichever Persona that you have obtained, you will be able to resummon them. So once you have unlocked Velvet Room in NG+, you will also be able to see the weakness/resistance of those Persona you have in Compendium. Minibosses and bosses will still be ??? though. 
• Items you get from confidants after the final boss. 
• All skill cards
• All equipment - Weapons, armor, accessory, as long as it's equip-able. Whether, it's equip or not, all these equipment will be unequipped and send to inventory in NG+.

What to do before Last Dungeon?

22nd Dec will be your last day for roaming. So you have to get these done before the next day.

• Try to fuse high-end Persona that can turns into high-end equipment. Persona don't carry forward, but equipment do. So I highly suggest you to "Itemize" them as much as possible before going to the dungeon. Do keep note you can only itemize one Persona per day.
• SELL ALL your treasures and consumable items (medicine etc). Turn them into money. Those materials don't carry forward. So instead, sell it to Iwai. You can use money to summon high-end Persona during NG+.

Events before NG+

Let me get things clear, you will get 3 kind of NG+ items after you beat the last boss. Confidant point booster on Christmas, SP-restoring chocolate on Valentine, and farewell gifts that unlocks confidant ability in NG+. Aside from getting these items, you can't do anything else except going through the story. So make sure you do it before 23rd Dec.

24th Dec (Christmas)

On this day, you will be able to date your partner. Whoever you dated, you will receive an NG+ item that boost the confidant points during NG+. For example, if you will to date Makoto that night, you will receive an item that boost her confidant points faster in NG+ when you have the same arcana (priestess) in your persona inventory. So just spend the night with whoever you would like to date, this item isn't that important to begin with. :)

14th Feb (Valentine)

Just like Christmas, you will be able to spend time with your partner. Despite who you are dating, you will be receiving a NG+ SP-recovering chocolate. It's even less valuable than the previous item honestly. If you are having more than one partner, you will trigger an additional event on 15th Feb where Sojiro will give you another chocolate. Hence a bonus, I suppose. So let me repeat, there isn't any drawback dating more than one girl.. Except the fact you should guilty. So go wild!

19th March (Farewell)

Then again, a lot of you keep wondering if cheating your partner will affect your NG+ items. The answer is NO. On this day, you will receive NG+ farewell gifts from ALMOST EVERYONE with max confidant rank regardless of you cheating on her or him. These items help to unlock some of the confidant abilities immediately at the start of NG+. So these items are far more important than the previous two. Make sure you check your map (R1>square), everyone that appears with max confidant will give you an item. This including Twin Warden/Lavenza. Despite you are able to roam around the town, you can't do much except talking to people/confidant. You can't even enter the Velvet room to itemize Persona or sell items on this day. So you have to do everything before 23rd Dec.
PS: Keep in mind Farewell gifts' effect will only activate after you have unlocked CR1 of that particular confidant.

Twins Warden's Battle

As mentioned, you will be able to battle with Twins Warden. Recommended level would be around 50+ level. Preferably the members you are using are at CR10 and learned Evade Weakness ability. During the battle, there's condition where you have to deal a certain amount of damage to the Twins after 6 turns. Otherwise the Twins will knock down your whole team and instant kill your team. The main reward winning the Twins is that you gain Omnipotent Orb, which null all elements except Almighty. You can re-battle with the twins anytime even if you lost the battle. 

Tip 1: It may not be a bad idea to lose to the twins if you are able to last at least 10 turns. The Twins will give you Expedite Ring, where you will gain extra 50% exp for equipped member. And it's applicable even if that member is benched, which it makes it extremely useful for character you are not using, for instance Futaba. 

Edit 23/7/17: More detail on Persona Compendium and Farewell gifts.
Edit 20/8/17: Added Twins Warden's Battle.