Prog. Metal Tips:Make use of uncommon time signatures such as 5/4, 7/8 etc. Some popular scale choices are Phrygian, Natural Minor, Harmonic Minor, Pentatonic. Also some bridges in long prog songs use some type of atonal harmonic structure.Create the first rhythm of your song using standard metal playing techniques and use lots of single notes as well as power chords. Avoid always using perfect fifth harmonies. Try using diminished, augmented and third harmonies as well.Make the riffs simple and easy to memorize but change the riff, time signature, scale and key often. For example, your first verse may have 3 different riffs in 3 different keys and time signatures in it. Change the drumming up, stress different beats in the bar than normal. Adding this all together creates the ever changing, complex sound of prog metal.Harmonize your riff in the correct key and scale.Since you will have lots of different riffs to memorize it is best to improvise all your guitar solos. This is beneficial for two reasons 1. it's easier for everyone to learn the song quickly as they will not have to memorize long and complicated solos. 2. everytime you play the song live, you will have a totally different solo, keeping the song fresh and new sounding each time.