Alright, all very basic.
1. Genjutsu needs creativity. You must be specific in what you do as a Genjutsu user as you need to affect all five of the senses and be able to use that to the best of your advantage.
There is something called the cause and effect,, an important of Genjutsu and nearly every battle. For example, you used a Wind Jutsu to blow away the explosive tag, thus, I can follow up with a prepared fire move to disregard your Wind Jutsu, so that it overcomes it and is sent back at you two times stronger.
By taking the upper hand, you can juggle your opponent around and have them react the way you want to, as we are all forced to make moves and survive in a battle. This is most often used in chess, where it is necessary to be able to predict several moves ahead of the opponent.
2. This also falls along the lines of knowing how to counter someone.
Alright, excellent.
Begin by sending out your chakra and then manipulate my five senses so that I am led to believe that I am somewhere else.