Tips for using early IR missiles

Im currently spading the Saab 105G and got the missiles yesterday. I'm trying to figure out what are the best situations to use the missiles consistently.

Against faster targets i had average results, i don't know if it's luck, the enemy being unaware or what.

Against closes and slow enemies in a turn, i never worked out and i don't know why, the enemy is pretty slow so they arent pulling lots of Gs, does the missiles need some distances before locking effectively?

The best way i used a missile knowing it was gonna work out i scared and enemy from below hopping he would go vertical, when he when close to stall i just launcher and got the kill he was around 1.8 km away.