To quilt by machine is a step by step process and you have achieved the first steps, STID, straight lines, echoing, etc. I am assuming that if you did echoing that you did it with the feed dogs down which freed your stitching. I concur with all who mentioned small projects so you won't be distracted by 'bulk' that has to be managed. Doodle and then quilt. Draw pictures and quilt them. Use stencils (one of my favorite ways because I have problems drawing) to mark fabric, then FMQ them. What you are after is even stitches and this practice helps that skill. I also liked to let the motifs printed on fabric to guide my stitches. I have benefited greatly from the website by Lori Kennedy-Inbox Jaunt. She also has a column in the AQS magazine and now has a Craftsy class. All of tha being said, the key is PRACTICE.
Good luck, come on in, the stitching is great.