U can tell if you are unbalanced by having too much or too little of a given element.
Being too emotional: too much water, lacking air
Way too much daydreaming, lazy: too much air, lack of earth
Agressive/Irritable: imbalance of fire, correct with invoking water
When invoking the elements, absorb them into your aura, chakras, or soul. You can picture ur body as being hollow and evoking an element to fill it.
Never direct it to an organ. Eg Fire into the brain, heart, or stomach.