I drive a 1996 Ford Mustang Gt. It has a manual transmision. I already know how to shift gears. I was just wondering what is the proper time to shift gears, as in rpms, normaly i shift the gears when it gets to 2 and a half rpm or i just shift after ever 15mph. Can some one suggest something better because i would like to know  

Just like in Star Wars, "use the force Luke......let go Luke".  It's all about feeling.  Forget you even have the tach and speedo on the dash.  Under normal acceleration the car (engine) will let you know when to shift it.  Like making love to a woman, you must become as one.  Ignore the gauges and just feel and hear what your engine is telling you.  The car will let you know if you are running it a little to high before shifting, or shifting to soon and making it lug a little in the next gear.

Honestly, it's all about what feels right.