I find that everytime I pick up my guitar I do a sort of review of things I worked on before, then I spend a fair amount of time on whatever lesson I'm focusing on at the moment. If I feel like I'm at least 80% there and getting bored, then I'll start the next lesson. But I keep going back and practicing the prior lessons at the beginning of my next practice session.
If what I'm working on is taking awhile and I'm getting bored or frustrated, then I find I'll go peruse the lesson lists and pick something out that sounds interesting and (possibly) within my skill level. So if I'm tired of working on practicing chord progressions in time, then I'll go check out the beginner fingerpicking course...or maybe one of the song lessons...or something.
I try to be vigilant about beginning my practice sessions w/ a review of previously learned skills, spending a majority of time on a focus topic, and preventing boredom or frustration by previewing the next lesson or another topic altogether.
For example, right now I'm focusing on the Guitar Fundamentals 2 lessons on mixing major and minor chords, specifically in time w/ the backing track. I start my practice sessions going through some scales and chord progressions from previous lessons that I feel like I know well...even if I don't play them 100% perfectly yet. As long as I feel comfortable enough to move on (knowing that I'll be coming back to it the next time). Then I spend quite a while working on those chord progressions to the backing track. I basically repeat them over and over until I'm bored or my hands get tired. I then finish my sessions off by checking out a new lesson...like Blues or a song lesson. It's not with the intention of getting it down pat or adding it to my daily practice...just to keep me interested. Like a preview of things to come.
I expect that as my guitar playing evolves, my practice sessions will evolve as well, but this seems to be working pretty well for me so far.
Best of luck!
