The golden rule of gear: Until you’re max level or have obtained living gear, your gear won’t last long. Don’t spend much time or gold on it, and do not spend a single gem on it.
When your primary goal is to reach max level, mix in some gear that boosts your experience gained attribute. Don’t overdo it, of course. You still need stats that allow you to kill enemies quickly. After level 70, your hero gains champion levels and points, which allow you to boost hero stats. Create a set of gear that boosts experience gain and use it when you’re trying to boost your champion level.
If you receive a chest with a set item (typically through the Reward Calendar), open it only with a max-level character.