I came across the image below and thought it was a great way to do a quick check of student understanding after a lesson.
I often had students put these self-assessments in their portfolios, but that is not always necessary.
Here is the link to this Google Form for you to use. Make a copy of it, and then you will find it in your Drive.
Update:
I came across this emoji exit ticket that I think is better. You will be prompted to make a copy of the document after clicking the link.