I ask this because oftentimes the guerrilla forces, even if they win in the end, tend to have a pretty negative K:D ratio by the end of a war; but in the IRA's case, they fared quite well. I mostly am asking for the tactics and strategies employed by the IRA that made them effective against the British forces.
They didn't?
The IRA of the war of independence consisted of 15000 men, of who they lost 550. The British forces had around 40000 men Inc local forces and lost 770. We also have a similar number of civilian deaths.
Both sides fought themselves to a point where they both believed their position to be unsustainable and the truce was signed by Michael Collins, who at that time believe the IRA was just a few weeks from collapse.
If you're asking how were they were effective, well popular supported guerilla forces and the use of tactics that dissipate technolocal and numerical advantages. Ambush, hit and run and surprise raids. It also should be noted the IRA splintered on the signing of the truce and continued to attack British forces, as well as slowly devolving into its own civil war.
Peter Cottrell - The Anglo-Irish War The Troubles of 1913–1922