In this guide you'll learn how to obtain high rank equips, and the best way to go about farming them.
S Rank Equipment
You need an average of good rolls on each of the 3 slots to have an S rank piece of equipment, if you have a slot or two with really high rolls (gold or red), it's much easier to get an S rank equip, but you can still have an S equip with 3 green slots (which is usually better since all slots must have decent rolls).
What rolls to aim for?
Rolls are the percentage you get between the minimum and max stats an equip gives, good rolls are usually within 2-3% from the max, but it varies between each equip depending on its range.
The best way to farm S rank equipment is to upgrade only the pieces that start with good rolls, below is what I believe are decent enough rolls for most equips to be S based on my experience:
8.5% out of 10%
9.5% out of 12%
10% out of 12.5%
12.5% out of 15%
14.5%-15% out of 18%
16.5-17% out of 20%
17.5% out of 21.5%
20% out of 25%
24% out of 30%
33% out of 40%
Gold and Red slots are always really good rolls.
How to go about farming them?
As I mentioned above, the best way to go about farming them is to start with good rolls, but you'll still end up with A rank equipment most of the time even if you upgrade them, and that's when you start looking at the other 2 slots. If you have 2 good rolls on a certain equip, you should try to reroll the bad slot till you're satisfied with the result, either with slot removers, or 10cc. If you have a red first slot, you could still reroll the other 2 slots, and it's alright if you take decent but not really high rolls on them, as it's still going to be possible to get an S.
If you aren't farming awakened equipment, sell all E equips, and only keep the D equips with good rolls, if you're farming awakened equipment, you can upgrade E equips till they're B so you can use them. It's harder to get S on awakened pieces of equipment, so it's generally best not to chase it, and it's because the good rolls are different there since the range is smaller.
Some equips are decent even when they're only A, so you don't have to always chase an S.
Z Rank Equipment
Z rank equips are much harder to acquire, and could be quite expensive as well. You need really high rolls on each slot, and you might still end up with an S equip with 3 gold slots.
What rolls to aim for?
Gold slots, red slots, and rolls that are really close to gold on the first slot. You can have Z equips with 2 gold slots and a green slot if the 2 gold slots are both high, you can even have a Z with a red slot and 2 green slots if both are close to gold, but you generally need 3 gold slots, or 1 red, 1 gold, and a really high green.
How to go about farming them?
You want to only upgrade equips that start with a gold or red slot, or really close to gold, and then only reroll the ones with double gold slots, or that are A rank without upgrading the last slot. If it starts with a red slot, you can still try to reroll it for a gold, or in extremely rare cases, another red, then work on the last slot. It may take a lot of CC and slot removers to get a Z even on equips with a red and a high gold, since you still need a high roll on the last slot
Cursed Equipment
You'll know what these are after you're 1k cc in rerolling them for not even S despite them having 2 gold slots, or when you spend all your resources for not a single good roll on any of their slots.
Just keep spending :)
How to go about farming them?
You should keep your standards low for them, might even upgrade ones with bad rolls for a chance of getting good ones on the slots you need.
I wouldn't chase a Z on them in any case unless you want to burn through your 3k skip tickets or 20k equipment medals, unless you're feeling lucky, then, go ahead.
Conclusion
It's important to set a goal when upgrading equipment, you could end up using all your saved CC on them if you're upgrading the wrong equips or if you're upgrading a lot of equips simultaneously in hopes of getting a Z or an S.
I personally don't recommend chasing Z equips unless you're satisfied with your team and you know you'll only be spending on specific banners and think you're comfortable spending CC and slot removers on them. I do that myself, and I can tell you that it drains a lot of my monthly CC.