What Are The Precautions In Taking Subcutaneous Injections?

I need some advice for subcutaneous injections besides the basic instructions that seems to be on most sites. My question, is the following: I have read and followed the proper instructions for administering a subcutaneous injection. When giving the injections to my mate, he almost always experiences minimal to no pain at all. However when I give SC injection to myself with simple water for injection (just to see what hurts and what doesn't) using the exact same procedure and the correct (?) spots, I experience a lot of pain and a little bleeding (more than what is considered normal for SC shots) so I am wondering what could I be possibly doing wrong? Could it be I reached the muscle tissue using an insulin syringe that comes with the appropriate needle? I inject into the upper part of the buttock. Note that I have managed to give a SC injection to myself correctly 2-3 times but in between and after these times the pain was too much so I stopped to prevent damage. The less successful and painless injections I can give myself, the more confidence I loose in being able to administer them correctly and painlessly to my mate. Any help would be greatly appreciated