man i remember my first heroin thread asking about how to dose.. shit takes me back.
good times... good times... (some of the best!)
be prepared for the nod! (altho you can't really prepare or anticipate it, it will grace you with its presence when it feels like it, whether your doing something like typing on the computer or not, so try not to smoke cigs or anything). the nod is awesome though, and it's like your awake and asleep at the same time.
also start very small. my first bag was fire as hell and fat as fuck, and i was able to nod heavy off of it 5-6 times, and i had a decent tolerance.
as others have said, i recommend not shooting ur first time. get acquainted with the drug first, and try either snorting it (may be kind of awkward/painful to snort, since you'll have to use an oral syringe to dissolve it in, and maybe a few other steps not sure, but you can search on here and find out what's necessary, and you basically just snort the watery liquid) or try plugging it. if you plug it tho, start very small as well, cuz this shit ain't no oxy, and is some heavy duty stuff. also, the peak will be much longer when you snort it versus when you inject it, which some people actually prefer.
also, don't keep snorting the H trying to achieve a high similar to oxy. there isn't as much of the "speedy-like" euphoria as oxy has, so you may not be used to what the high really feels like at first and accidentally do too much. this kind of happened to me, and i woke up like 2-3 hours later on my keyboard lol.
also, you may not really enjoy the high it produces as much at first, but trust me, the euphoria turns out exponentially better than oxy once you get accustomed to the different noddy-like euphoria it produces, and just overall contempt with any situation.
one last note: sounds like you've been using opiates for quite some time. heroin will grab you by the balls like none other. you'll put that shit away in your drawer and it'll be calling your name all day. be careful man, and try to take breaks if you can. always test out new batches, this can save your life.