Hi,
Ref strumming and embelishing with riffs. I struggled with this for a while, but what helped me was learning scales, particularly
majors, minors, blues and pentatonics.
Try to learn the patterns rather than the notes other wise it can be baffling. Learn the notes on the 6th and 5th strings helps with root notes.
Lastly, find a song you like on CD, find what key its in by playing root notes at the beginning as most songs start with the chord for the key it is in. Lastly, play a scale in major or minor to work out which one it is. Then you can play scales and riffs over the track. Its good fun and its a bit like playing with someone else, which I always encourage anyone to do.
Suffice to say in the end its about practice, practice, practice!!!
Happy pickin'