When using a nasal spray, the main thing to remember is that once you have inserted the nozzle into your nostril, the spray should not be aimed at the wall in the middle of your nose. Instead, it should be aimed towards the ear on the same side (see diagram).
Blow your nose beforehand. Tilt your head slightly forwards and breathe in gently with each spray you give.
If your nasal passage is narrow, it may help to pull on your cheek to open your nostril.