Equipped gems also level up as Path of exile currency you earn XP, getting ten percent of the base XP awarded from monster kills. Your character encounters an XP penalty when revisiting lower level areas, but that penalty doesn’t apply to gems. So you can certainly level gems by replaying areas that are a few levels lower than your current level.
Every part of loot you get takes up varying levels of space in your luggage compartment. To take as many potential things at once, you need to move items around and squeeze items into the allotted spaces. Even then, your luggage is bound to fill up quickly if you pick up each and every thing you encounter.
The trick, then, is to discount items your character can not utilize or are of low price. Item rarity is indicated by colours: White: Regular, Blue: Magic, Yellow: Rare,Orange: Particular.
You can pretty much ignore white items unless you’re going to go back to town and have the space to spare for them. Rarer items are usually worth picking up and promoting, even if you have to hold onto cheap poe currency them for a short time. And needless to say, any product that appears better than your existing equipment is worth grabbing — even if you have to drop something else temporarily as you equip it.