Prepping for class... or the lack of

How do I usually prepare for class.  That all depends on how I am feeling honestly.  After going to class during the day and then going to work right after until about midnight.  I usually don't feel up to doing all my school work.  Usually I will skim over the readings just to try to get a good idea of what the reading is about.  It is a bad habit that I need to kick and make myself start actually reading rather then going to bed.  As for the class contribution since all I did was skim over the assignment I will only contribute if it is something that I am one hundred percent sure that it was something I read.  I have noticed that when I actually do read the assignment and contribute to class it helps me with my classwork/homework because it is helping me to pull stuff out of the readings rather then just read to say I read the school work.