Don't over call,when a bull awsners back and is coming,call now and then to get his location and movment.If call a couple time and he calls back and is coming and then all of a sudenly shuts up,DONOT move,check the wind,get your bow ready and your eyes peeled,he's close and checking out for the cow he heard.

Also if you call and getan answer to your call(say you usinga cow call),don't change it unless he hangs up.The bull my brother-in-law shot last year was this way.We bugled twice and nothing,cow called and he came running,you could hear the trees and brush snapping and cracking,he stopped 80 yds away cow called again and he ran in to 7 yds,turn and walk about 10 or so yards out turned braodside.That gold Tip sailed through him and landed another 20 yds the other side,he didn't even feel it.
Another thing,when I bugle I try to sound bad,hardly call with a challange,always a weak squeal,or a short bugle.I will usaly whack trees and stomp my feet,rub the bark,make it sound like I'm a young bull all worked up,follow with fighting cow and excited cow/calf calls,then a screaming bugle.Make'em think here is a young bull with a few cows that are hot but not ready,add a little sexual fustraion on his part,throw up a decoy and wait cause here come my hat rack.

I'm one of those guys that has about 10 calls on him,I will cow call with a diaphram,and havea hootchie in one hand and squeeze me in the other and a hot lips haging on my neck,don't be afraid to change it up.
BBJ