1) Start broad and narrow down from there
2) Give Google Scholar a try to see what is coming up
3) Step outside your discipline and consider applying techniques or approaches from other subjects
4) Read to learn the terminology which will influence what your keywords will be
5) Try "SoTL", "higher education", "postsecondary" if your results are primarily in the K-12 literature
In ERIC for example, you might find you're getting results related to K-12 teaching and will need to add terms to narrow to higher education.
The following list is a starting point to help you find SoTL research.
The search tips on this guide are adapted with permission from The University of Calgary's Scholarship of Teaching & Learning guide, and from The University of Connecticut's Scholarship of Teaching & Learning guide, shared under a Creative Commons 4.0 License.