Don’t Use Your iPhone While It Charges
This should be a given, but try not to use your iPhone while it’s charging if you want it to fast charge. That way, it won’t have to waste power as it’s trying its best to charge.
Not only does using your iPhone while charging not let it charge as fast as possible, but it can also potentially damage your iPhone’s battery if you do it too often. Overall, it’s best to give your iPhone a rest while it’s charging.