How can I execute a good screen pass, and how can I execute when the defence is in cover-3 with a line-backer (the user) is defending the middle?

Many people use screen-passes. I can stop them, yet I cannot execute great ones myself. I don't love the screen-pass. Matter of fact I find it noobish, but sometimes I like to use it to slow down heavy pass rushes. What is the best way to execute one?

If a player uses a d-line men, corner-back, safety or whatever, I can shred his defence apart. However, when somebody manually controls a line-backer in cover-3, it is very hard for me to execute pass plays. What's a good scheme to overcome this?