Although, there is no perfect way to tell someone how to play more interesting leads and solo's. You have to build on it by practicing. I can tell you most metal solo's are based around Modes. Modes are made from taking a scale, say a major scale, and instead of starting on the root, say starting on the 5th interval in the scale. Which is a Mixolydian mode, great for soloing over V7 chords. Its not just limited to a couple of notes in a scale, all scales and each note of a scale is a mode. Search though this site, you will find countless threads about this.

You must know the chord progression, which your soloing over. That way you can pick the correct scale to play over it. Most solo's sound lame cause they're using the same scale thoughout the solo, you have to mix it up to make it sound more interesting. Giving it a sense of flow, and movement rather than being stagnate.

A good way to learn how this all works is learn a song you like with a solo in it. Learn both the rhythm and the solo, then figure out how they come together. Take alittle Music Theory so you can understand how it works, there's also alot of threads and tricks on here just use the search to find them. You will find alot of pointers.