Let's face it--no matter how much you love garter stitch (I love it A LOT), sometimes in the midst of a very long garter stitch project (especially a rectangle or square without any shaping), it can be a challenge. You knit and you knit and it can feel like you're getting nowhere.
To give myself a reference point so I'll know I AM getting somewhere, I put in a marker when I pick up the project for the day. When I put it away at night, I can see, "Oh, hey, look. I knit 400 inches of this today." Sometimes I exaggerate.
That simple step helps me enjoy my garter stitch project much more. This can also be helpful for any other all-over pattern stitch that seems unending: stockinette stitch and seed stitch come to mind. Just put a locking stitch marker on your project, attached to the yarn so it won't get moved up each row, and you'll know at a glance how much you have managed to knit since you started for the day. You can also use a small piece of yarn, in a contrasting color, tied on in the same manner.
See? Progress! Yay!
Try it on your next basic project and see if it doesn't give you more of an ongoing sense of accomplishment!