I vary my approach based on trying to work out where the problem is. I spent about ten years as a professional illustrator, so I had to get pretty good at working out how to motivate myself when I really wasn't feeling it. My advice is, art block is not a magical curse. There's usually something behind it like apprehension about drawing something hard, dissatisfaction with what you're making, or just your body needing something.
If my attempts at drawing are slow and timid with stiff lines, warm up sketches are usually the way to go.
If I feel demotivated about just making comics in general, I read other peoples' comics and talk to friends or my fiance about comics to get myself feeling fired up about the medium afresh.
If I feel lost, like I don't know how to approach a particularly tricky pose, or I have to draw something I've never drawn before, or that I find hard (like horses and cars, aaaaaaagh), I look at my collection of tutorials or look for reference on Pinterest.
If I just generally feel lacklustre and have no mental energy, I step away from the computer and do something like: exercises or a little yoga, household chores, sing along to a song I like and have a nice cup of tea. Sometimes my brain just needs a little break or my body needs hydration, minerals, exercise etc.