Path of Exile is all about the PoE items and how they can enrich your experience, so it stands to reason that you pick up the loot that gets dropped by the monsters you kill. However, with limited time and inventory space, you can't possibly pick them all up every time, so you will have to get your loot priorities straight and pick up what will be most useful.
Whatever, the forms of Path of Exile Currency, unique items, quality skill gems, and three-color links should be picked up. Generally, whether for equipment or trading, these are the most valuable poe items as they add value to your character. Most of them are easy to know, including the 3-color link socketed items that are composed of green, red, and blue sockets.
Although, quality skill gems are not obvious, especially for new players as they have skill gems already that have been leveled up quite a lot. But quality skill gems are quite valuable and players should gather without hesitation. For using, even when under leveled, they perform better than normal skill gems.
Not as necessary as the top priority items, they are very valuable and should be picked up when you have the opportunity, such as rare items (PoE Exalted Orbs), max implicit items, high links, and non-quest skill gems. When you pick up them, you can either use them or trade them, both of which should get good results.
High links are 5-link and 6-link items that you can pick up, and 4-link ones are only necessary if there's nothing else better. The 6-links are rare enough, so remember to grab them no matter what. With max implicit items, make the same as implicit values independent from other stat bonuses, which give perfect implicit mods a quite high value in PoE.
It is not important to compare with the above ones, they should be picked up if necessary. Magic flasks, advanced flasks, and irregularly colored sockets items form this middle tier, which seems to be the utility. The socketed items are those socketed items who have not been linked, in order to make use of gems, they have to make with these socketed items. When they start to get linked socketed items, they become for vendor recipes. The flasks are useful, but they really don't deplete much, so not as much demand for them.
There’s something else that you can ignore, such as white items without sockets, blue items, and quest skill gems. Usually, they are not worth the trouble for reasons that are enough in the long run. While they are useful for players who may know nothing about the game. For the most part, they are learning tools for beginners to ease them into the game.