How do I catch some? Traps? Anyone good at this ?

Get a little minnow net, go to a stream,river or lake that you can wade in. Use you hands and start flipping rocks, when you flip one with a craw he will scurry under another rock. If you see what rock it went under, take your minnow net and scoop the whole rock (if its small enough) or just scoop underneath. I usually just carry an empty water bottle and put them in there. The little river i go to i can catch a dozen in just a few minutes. There is a thread on here of a guy using a Soda bottle as a trap and it sounded very impressive and easy to do, you might want to search.

find a creek, and start flipping over medium sized rocks, and you WILL find crawfish

I haven't tried since I was a kid, but flipping over rocks we found them all day.