The Alternate Picking is a Guitar Technique that has been massively used since the 80s. Some Guitar players have made of this technique their Signature. Malmsteen, Al Di Meola, Vinnie More, John Petrucci and many more. The Alternate Picking is a really useful technique for Fast Picking and Solos. One of the first book I came across when I was a kid was the Troy Stetina – Speed Machine for Electric Guitar. I would definitely recommend you to have a look at that book. It works!!
In a nutshell the Alternate Picking is a technique where the right hand perform a progression of downstrokes and upstrokes. Usually always associated to fast picking, this technique can be used in many different approach. Let me put down an example.