I'm just going to echo what everyone else is said, along with my personal experience with atropine. Don't do it. You'll likely regret it if you do, and if you MUST do it, have a trip sitter with you at all times. It's not improbable that you might strip off your clothes, run through a window, and start talking to people that aren't there. Frightening the shit, of course, out of the people that ARE there.
I played it safe, and I did it out of curiousity. I'm not unhappy I did it, but it's not an experience I'll repeat again. Due to different concentrations of varying alkaloids, the experiences with different plants vary in effects and in dosage. From what I've heard, Belladonna is the freakiest of them all (a common visual is seeing people with their eyes blackened out, and viscous black bile or worms coming out of their mouth. I can't even imagine). You're also not coherent when you do it. You'll loss ALL sense of time, and constantly forget what happened from one moment to the next. Even if you realize you're tripping, you'll forget it in just a few minutes. You probably won't even be able to tell the difference between nighttime and daytime.
Smoking non-existent cigarettes and having detailed conversations with people who aren't there may sound like fun, but it isn't. There's a very sinister feeling to the whole thing, and you can't control your own actions. And you'll remember very little of it immediately afterwards, which would be horrifying if you woke up in a jail or a hospital. Also, be aware it usually lasts for a long time. Often as in days, not hours. And most importantly, be aware that it can kill you. Very easily. Content varies from plant to plant, and even leaf to leaf. It's -extremely- easy to overdose if you're not absolutely sure what you're doing, and I'm sure that you're not sure. And there's no coming back if you fuck up. You'll either die or trip for days at a time. Neither is fun, I imagine.
But, if you do intend on doing it despite all of this, be safe. Don't go outside, and have someone sober with you. It's very easy to hurt yourself or destroy your personal property, as you're not consciously in control of what you're doing. Dosage varies wildly, like I said, but you can generally estimate it. It varies by plant. When ingesting Brumansia, for example (a type of tree datura), 1/2 to 3/4 of one of those flowers is enough for full blown delerium. This is what I ate. If you're dead set on doing it, start with a very small amount. It doesn't take very much, and every part of the plant contains atropa alkaloids, from the flowers to the bark to the seeds. A common mistake is that people don't wait long enough for the effects to kick in, or don't realize it's working, and eat more. Big mistake.
So, weigh your options very carefully. I know it's hard to obtain psychadelics in India (if I read correctly, and that's where you're located)... But dying really isn't worth it. Take a little road trip and go hunting for some Indian Orisha psilocybe cubensis. That will actually be worth your trouble.
~Ethno