by using Kai's but those only work for B-rank and under
you can "see" through genjutsus with sharingan
the last option is through pain. When you stab yourself or what not, you can use the pain to get your senses back in order
Also, don't forget that an outside ally can "inject" chakra into you. The kai option works because you're focusing to re-orient your own chakra. Well, this option works because an outside source is orienting your chakra flow, which ultimately makes it more effect and easier to pull off. Most often people use clones to do this, although if you have an actual ally like in a two-on-two battle, they can also do it, or if you have another persona within you like jinchuuriki have bijuu within them, that also works.
Annnnyway, since I can't think of any exercises having to do with genjutsu, nor do I see the reason to have you meditate for a post or two, let's jump right into it.
So... first up.
Genjutsu: Kokohin (Illusion Technique: False surrounding)
Rank: D
Type:Supplementary
Range:Short
Chakra Cost:10(+5 if you use it double)
Damage Points:N/A
Description: The user controls creates a false surrounding which can change the way an object or small area looks(if used double then its a layer of false surroundings not easy noticed by the enemy).
Genjutsu perhaps in its simplest form. Genjutsu consists of focusing chakra into your opponent's chakra flow, mostly within their mind, and using that chakra to alter what they see, hear, feel, etc. You alter what is in their brain to the point where they cannot differentiate the genjutsu with reality. For this one, focus chakra into my mind and make me see something that isn't really here. For the sake of simplicity, try to make me see a tree right in front of me. Build up your chakra, and then focus it into my mind.
I hope that made sense. o.o