It would help to know your relative level of progression. Specifically,

• What chest from CB do you get, daily?
• What level of Dragon and Spider are you able to clear reliably?
• Have you been able to advance through Doom Tower? How about DT Hard?
• How far into Faction Wars are you?

I do have nitro on discord so I can stream my progress for you if interested. I think you'd find my spider progress most abhorring. It's to the point where champs that really should have accessories, don't.

• Ultimate Chest from Nightmare Boss in 3 hits, close to 2 hits. Hits are 14M-19M.
• Dragon 20-22 reliably(EDIT: 23 still not reliable). Spider 17 reliably. Could probably push it further, I have a few champs that'll help me do so when geared.
• Doom Tower is easy to progress in for the most part, but Scarab King is usually what stumps me. I have few shield heroes and swapping for Destroy sets doesn't seem viable for a single boss. I can clear ~up to the first boss on hard DT.
• 6 factions over 25 stars. I have only defeated the 2nd boss in 2 factions. 294 stars total.

Okay. So in that case I'd say you'd be safe to use the following autosell rules:

• Everything under 5* - though if we want to be really aggressive, honestly, everything under 6* is probably a better choice
• Everything under Epic rarity, with the possible exception of Speed/Perception sets - although, again, I think you'd be safe to sell the rare speed/perception too, given that speed is not really in-meta anymore
• Bottom-row flat primary stat. For the remaining items, Epic with two flat substats, Lego with three flat substats.
• For accessories, ATK rings without ATK% substat. DEF/HP rings without either DEF% or HP% substat. ATK Amulets. DEF/HP amulets without RES and ACC. Keep the rare+ items for accessories, since they're a bit harder to come by.

I would actiually keep atk amuletts from factions where you have bomb champions, especially if you roll them to 8 and get a bonus to accuracy substat.