Before NG+
Pretty much a checklist for this: New Game Plus Elden Ring Wiki. This checklist includes everything you might want to do before starting a new NG+ cycle.
- Back up your save file (just in case)
- Hand in all Bell Bearings to Twin Maidens
- Collect as many final Upgrade Materials as possible
- Farm Runes to buy out the Merchants' shops
- Collect all Cookbooks
- Collect all Cyrstal Tears
- Collect all Whetblades
- Find and turn in all Scrolls and Prayerbooks to a trainer to purchase their Spells
- Slay dragons to obtain Dragon Hearts (23) and buy their Incantations at the Cathedral of Dragon Communion (only 20 are required to purchase all Dragon-based Incantations)
- Obtain all Larval Tears (18) for future Rebirth
- Turn in all Deathroots (9) to the Gurranq Beast Clergyman
- Kill any NPCs you want the gear from
- Collect Stonesword Keys
- Trade for any Remembrance Weapons you may wish to dual-wield in the future
- Obtain any weapons you will want to dual-wield in the next playthrough
- Use Walking Mausoleums (7) to duplicate Remembrances
- Collect all non-renewable Crafting Materials
- Collect all Cracked Pots
- Collect all Ritual Pots
- Collect all Perfume Bottles
- Collect all Memory Stones
- Fully upgrade Sacred Flasks
- Collect all talismans
- Farm any Weapons or Armor that drop from Enemies that you might want (optionally respec for Arcane to increase item discovery)
- If you plan on playing with a different build on NG+, pick up any equipment for your new build
- If you plan on playing with a different build on NG+, respec your character by talking to Rennala