drop in mileage

Hi everyone. I've got a 2001 Mustang, V6... I've noticed that recently the mileage has dropped way down. Last I checked, about 6 months ago, I was getting around 21mpg, now I'm getting 14mpg. I notice that sometimes while I am driving that the needle moves up a little, and whenever I start the car the needle is down/lower than when I last killed it. Does anyone have any ideas?

What needle are you talking about? I'm sure its the needle on a guage but what guage?

the fuel gauge

the fuel gauge

Well, the guage is going to go down when you turn the car off. It happens in just about every car ive ever driven. So i'd say thats normal. As far as fuel mileage..
(1) Dirty air filter
(2) Bad plugs/wires
(3) fuel filter
(4) Dirty injectors etc