I've never done heroin, but like the posters above, my first bit of advice is - don't do it.
Although I have never done heroin, I have done other opiates, and luckily have only ever had a limited supply so never had chance to get addicted, because a regular supply is not possible for me, neither do I want to make it possible.
I hope I am not sounding self-righteous, I have experience of other addictions - speed and benzos. Off the speed now, but only because I had no choice, the benzo withdrawals meant it pointless me using speed.
From the many others I have seen, it is impossible to dabble, due to a special characteristic of opiates whereby you just cannot help taking more.
The saddest thing is that I have heard one person coming off opiates say "Is this as good as it gets?"
Heroin users who want to get off heroin seem to need to take drastic steps to stay off it, such as re-locating away from heroin using friends, who try to get you back on the stuff relentlessly.
From what I gather from many heroin users is the psychological diffficulty in staying off.
I know I sound negative, but the most positive thing is, realizing that no one can get one over on lady H, she is a true bitch, and steering clear.