I usually do some hand stretching exercises first. Then I make sure the guitar is in tune. I practice scales after that for a warm up. How long you do that is up to you..

Then I work on whatever lesson I am on.When I get tired of doing that, I shift to learning a song,I always have one to work on. That way when the lesson gets tedious you can take a break from it,then go back to it,instead of frying your brain.

This may not be the right way to do it,but that's how I'm doing it at this point. I'm sure there will be better answers for you from more experienced musicians.

Keep practicing...... :cool: