Get on Youtube and search Scott Ellis with Woodhaven Calls.
He has several videos of how to and is VERY good at calling along with explaining how to run calls, especially diaphragm calls.
Practice, practice and more practice!! Keep one in your vehicle and on the way to and from work/school whatever keep trying. Atleast this way you wont get thrown out the house or cause a divorce!
I started with a pot call and then a mouth call, now days I utilize a mouth call more as I have developed a control issue with my hands. I'm having trouble controlling the striker, I do it when I write as well. It's almost like parkinson's disease, I develop an erratic motion when I try to maintain a rhythm or write.
I have been tinkering with a trumpet and would love to master them!