Read the Codex. if you don’t know what cool stuff to farm for, you wont make a farm build to get it.
New Players are stuck with low tier Crystals & Myth Stones, and random items. the 2 most important Crystals for New Players is Angelite: give 1 random Normal (Yellow) or Epic (Orange) affix, and Kyanite (remove one affix of your choice. works on Normal, Epic, Legend, and Set affixes). Calcite is good for changing your items Elements when needed, but with Angelite & Kyanite, you can make a set of Equipment that doesn’t need to change Elements, so you can use an Element you like all the time.
when using Angelite to put affixes on Equipment, the sixth affix will always be Epic, so if you have 6 random Epic & Normal affixes on an item, if you take one normal affix off at a time and use Angelite to put an affix back on, it will automatically be Epic.
for the Beginners Farm Build, you put an Epic Luck and Gold Find on each item. if you have a Pet, you put those on the Pet also. when you get Hero Points, get your Fortune Skill up to 20. also, if you can, find items with Luck or Greed (Gold Find) Natures, 3 of each. doing this will get you to +650% Cap for Luck & Gold Find on Very Easy Difficulty. Very Easy Difficulty is the easiest Difficulty to kill monsters, which is good since so much space is taken up for farming. three or four affixes of Elemental Weaken is the affix you need so you don’t have to keep using Calcite and you can keep the Element you like to use.
any spaces left over can be any affix you want, which is a good way to discover what other affix do.
when you find Legend items, you can do the same thing. some Legend items have an affix called Fortune, it can raise your Fortune Skill up to 40, so you only need 1 item each with Luck & Greed, giving you the chance to use other Natures to improve your Equipment.
items with Sockets can have Myth Stones placed in them. affix values are based on the items level, so low level items will have lower values than higher level items. Myth Stones are like an affix with max values no matter what level the item is.
going to higher difficulty levels means you need less space for the Luck & Gold Find, but the monsters are harder to kill and they do more damage to you, so it is a trade off. better to learn the game and farm Very Easy for better equipment before playing on higher difficulty levels.
Pets cost 5 Crystals to use affixes on them. if it takes 5 attempts to change your Pets Element from Poison to Shock, it will cost you 25 Calcite.