The best way of self injection is to use the right size needle
and choose the correct spot. For Streptomycin, usually given intra
muscularly, use a thin needle (23/24 guage) and select a spot on
the upper, outer thigh (no major nerves or blood vessels there). 
Clean the area with antiseptic before injection, and after. Make
sure to inject deeply (a different kind of pain is felt when the
needle enters the muscle - contrasted to the 'prick' when it 
pierces the skin).