Once you have a research question, share it with colleagues outside your narrow discipline and ask what bodies of theory they would draw on to make sense of it.

Read widely: theoretical insights do not just come from readings in your topic area or discipline.

If theoretical papers and books seem difficult on first reading, try skim reading to get an overview, and returning to them later, when you have some empirical data from your own study to peg the ideas on to.  

Practice using middle-range theory by seeing if you can describe your (or others’) findings without mentioning the specific health care setting, or practitioners, or health conditions of the study, but instead using terms to describe the phenomena those settings, practitioners, or conditions are ‘cases’ of.