Since I have NO WAY of telling how potent your heroin is, yes, just take bumps, or as I call them sometimes, tiny lines. thats really the best advice I can give..
...actually, even better advice would be to have a friend who actually knows what there doing with this stuff, show you the ropes. Hopefully he/shewould be able to tell you how strong the dope that you bought is, and therefore how much to do....hell, you could even ask your dealer how much to do....just tell him its your first time and you dont know.
Anyway, my main point is that the best place to get advice on how much of YOUR specific heroin to do is not over the internet. We need to see/taste/smell/and sample the dope to tell you a reliable answer....anything else is speculation, and speculation could kill you if we speculated wrong....these are hard drugs were talking about, not allergy medication.