You would not be getting the shot of insulin your body was expecting... So levels would go higher.
The 2nd..not alot else unless you put injection in your main artery or vein. Pump users will accidentally get air in to them .. We just get get raised levels for a while.
Hold the pen or syringe upright and tap the insulin a couple of times until the bubbles reaches the top, keeping the device upright draw up a few units of insulin and do a air-shot to clear the bubbles.
Air bubbles at best may leave a bruise or small lump under the skin which will disappear over time.