Taking street drugs of unknown purity is never safe, and there's never a good reason to get started with H, nothing good will come out of it. Also, if you can still get proper off just 10mg of oxy, just keeping on going with that, seriously.
However, if you must do it, there are some things you can do:
1. If it's powder, chop up a bag into a bunch of (maybe 6) small lines. Snort one, wait for 20 min, then go for another, wait again, repeat until you get where you want.
2. If tar either: a) Chase it off foil, don't have to put the whole bag on foil, but in any case you're not likely to OD. Titrate up to a nice place.
b) You can waterline it (dissolve the H in water, then use a syringe or eyedrop or something and drip it into your nose. You'll want to use as little water as possible, and don't put more than 5-10 units in your nostril at a time to avoid losing any to the drip), same titration rules as snorting powder.