Pablo, do you read music and/or tablature, or are you just watching videos and picking up riffs?
The latter is fun, but you'll become much better if you learn to how to do your own....
I read music. I feel like tabs is (are) cheating, but I do it if presented in that format. I can't hear a riff on computer speakers and know the notes. But I must still hear it many times and practice to get the rhythm correct.
In that case, Jaco Pastorius *swore* by Bach's Cello Suites as a development exercise. They'd be available in any music store that sells sheet music. They're also available here as .pdf's. Not exactly rockin' out with your [censored] out, but if like to be challenged, this is for you.