Most effective and cheapest - Pull it out by hand.
I've noticed the root system is shallow.
I have heard that it's an Annual Grass, dying each Winter.
It's the Seeds that survive.
May or may not be true.
When I pull it in the Fall, I'm very careful of not loosing any seeds.
When pulling in the Fall, look for purplish colored stems.
And Crab Grass does have a lot of seeds.
A good thick lawn helps against crab grass taking hold.
It needs sun-light.
Also, in the Summer, I cut my grass to a taller height (about 3").
Good luck.