There are many different types of items that drop in Diablo 3 but 99% of them are worthless. Finding those high-end items is what the game is all about. At this point in the game, many of the items in the game are not even worth picking up. Start out by finding gearing your character for the monster power and farming route that you choose. Most of the best runs are found in act 3 on low monster power, depending on your character's dps and survivability. The idea is to find the fastest route with the most enemies and the highest magic find possible. You will want to find a balance between these to make your runs more efficient. Farming on a high monster power will give you high magic find but will slow down your runs significantly. Farming on the lowest monster power will be much faster but you will have much lower magic find. There is no right answer to which monster power you should farm, it will all depend on your damage output, survivability and play style. Once you get your Diablo 3 farming route down, use this guide on which items to pick up and which ones to leave on the ground.
Lets start with the obvious, Legendaries. Since legendary items have been buffed, many of them can have amazing stats or can be turned into brimstones to sell. Some of the best legendary items ever found have sold for billions of gold and thousands of dollars.
Gloves - can have great stats since they can roll critical hit chance, attack speed and critical hit damage. This means that it is much easier to find a perfectly rolled rare pair of gloves than perfectly rolled legendary or set gloves. There are few legendary gloves that will beat a good pair of trifecta rare gloves.
1 Handed Weapons - You should always pick up 1 handed weapons in Diablo 3. Most of them will be worthless but they have a chance to be the highest priced item in the game. Rare 1 handed weapons with good stats have been sold for upwards of 20 billion gold. You are looking for a weapon with high dps, open socket, high critical hit damage, life steal and high primary stat.
Bracers - Now these are harder to sell but still have a good chance to roll very well. The only problem with bracers is that many players are looking for Lacuni Prowlers or Strongarm Bracers which are legendary items with stats that do not roll on normal rare bracers. To sell bracers you need high crit chance (5.5%-6%), high all resist (70-80), very high primary stat and very high vitality.
Rings/Amulets - These can roll as good or better than any legendary item in the game. Just like gloves, rings and amulets can roll critical hit chance, critical hit damage and attack speed. But they can also roll average damage and life %. Good rings and amulets can easily sell for hundreds of millions to billions of gold.
Pants - Many of the best player in the game still use rare pants because legendary pants with better rolls cost hundreds of millions of gold. What you are looking for in a good pair of pants is high primary stat, high vitality, 70-80 all resist and 2 open sockets.
These are some of the best items to pick up while farming in Diablo 3. The reason most people do not pick up 2 handed weapons, crossbows, chest, helm, etc is because there are many legendary items that, even with bad rolls, are better than most rare items. These legendary items are best in slot for the most part and players will not waste their time or money on anything else. That being said, there are plenty of items out there that are not on the list above that will still sell but for much less. If you are trying to cut down on time and increase efficiency, I recommend only picking up the items listed above.