Usually for memorable solos simpler is better. It can take a lot of belief in yourself to play something that's not super flashy but really fits the music. There's no magic recipe though for a great solo... you can learn all the scales, licks & tricks in the world, and still end up playing something that doesn't really connect with listeners. You just have to be yourself and allow your own uniqueness to come through. Its not hard rock, but listen to the solo by The Edge from U2 in "New Years Day". First off, you can hum it... secondly, I doubt he really gave it much conscious thought as he came up with it, but virtually the whole solo is played on the off-beat. Also notice that he uses a very in-effcient method of getting from note to note by staying more on one string and sliding from note to note rather than switching strings, but the sliding from note to note really makes the solo. These are things that he probably didn't think of so much technically, but just thought sounded good.
You can't sit down with videos & text books and map out the perfect solo using mathematics. Just allow yourself to tap into your creative side, put the theory away for the moment, and see what you come up with.
