Be mindful of how much inventory space you have. If you do not pay attention it will fill up, possibly preventing you from picking up additional items, completing quests, and you could become over burdened and slowed down.
Items placed into the inventory take up space (inventory slots). Initially the inventory is small but as you complete quests you will be able to expand the number of item slots. You can also purchase inventory space via the Pearl Shop.
In addition to space needs items also have weight. If you reach 150% of your weight limit you will not be able to carry additional items, even if you have an inventory slot for it. If you carry a trade good the item will not only take up an inventory slot but will be displayed as being carried on your back. This will significantly slow you down - independently what your weight limit is - and prevent actions like fighting or gathering.