Great Stuff! I am looking for a new lens myself... but I really dont know what to look for... heck I didnt really know what I bout when I got my canon rebel xti

... can anyone tell me if these lens I got with the camera are any good..I though I got dooped...but I didnt really know what I was looking ...maybe the reason alot of my pics appear soft on here
Tamron AF 75-300 1:4-5.6 LD TELE-MACRO(1:39)
Canon Ultrasonic EFS 18-55mm
Is there a general rule for picking lens for certain shots... such as portraits?