Subcutaneously. Get some insulin needles and syringes and inject into your belly skin, but do proper research into exactly where and how to do these shots. I'm sure there's info on this site about SQ shots.
With HCG there is almost no difference in the effectiveness of intramuscular vs subcutaneous but also prefer subcutaneous. Lots of studies have been done to compare.
Ovidrel (rHCG) might be slightly more effective with intramuscular injections. According to studies done for Ovidrel's official biopharmaceutics review IM injections were found to be more effective in men. But for pct purposes it shouldn't matter.