I'm reading the same questions all over and over again in many forums. "Why is my farm so low?", "What do I do with this class?" , "Where do I farm?". This will give you a decent introduction on how to farm as a beginner.
Where to farm?
There are several spots, every one of them unique and different. Since gold income is situational, you'll have to find a spot that suits you best. However, when it comes to efficiency, the best public spots would be Act 3 Qeust 7.3 NM or Act 1 Sarkoth Inferno farming. This will change, there will always be farmspots, nerfs and new farmspots (just like Royal Crypts that got nerfed few weeks ago). Spots will come and go, so be up to date.
Factors you should NOT underestimate
There are at least two vital factors that'll influence your
First crucial factor: Gear; Goldfind should be around 300%, PR should be 20+ and movement speed 12% [at least] + some passives/actives (Barbarian/Demon Hunter etc.).
If you're ranged, your Pickup Radius should be 30+. If you're meele, 20+ are decent since you'll physically interact with most objects.
Second crucial factor: Your skillbuild. You shouldn't just spam every slot with random spells. Try several builds, reset your stats and find the perfect high. Your passives are as important as your actives.
~ Happy farming