I do!Hum, that is harder because I've never fought anyone using genjutsu, and it's very rare to see fights where it is used, even though I try to use every category of jutsu, I think I've only used it a couple of times.
There are always some tips to know if you're in a genjutsu or not, right? Your head should feel weird, since someone else's chakra is messing with it... Also normally Genjutsus affect only one sense, from what I've seen. Normally it's only the sight of the user that is affected, correct me if I'm wrong, since I'm entering on a pure speculation zone.
Being a hunter in one bio, I'm used to see every move, every expression and also every sound made by the one I'm fighting. Even if I don't react automatically, I'd easily get that I'm on a genjutsu and I'd force chakra on my head and blast the presence of the caster right away. but I also like to appear to have been affected. People usually feel safe and let their guards down when they use a genjutsu, so if they still assume we're in the genjutsu, we can counter attack efficiently.
There's another thing. Usually animals aren't affected by genjutsu. Teca wouldn't be affected and she could bark (or w/e sound foxes make) to snap me out of the jutsu, or ultimately bite the opponent to make him loose concentration and release the gen.
Against sharingan user, I don't usually look to their eyes. That can be both a downside and an advantage. Do you have any tips for those cases? I mean, you must be brighter then Guy Sensei...
Sharingan users may be able to see your chakras, but the cannot see through solid objects.
Try and block their vision for a moment to unleash a devastating attack they did not expect.