First: read the literature, and search for something interesting to you. Search for question posed in the literature (check the discussion section: "and future research...")
Then, define CLEARLY the research question
Has been answered before? Read the literature
Yes: check the methods: can you do it better? are the results valid? applicable?
No: is feasible?
What data do you require to answer the question?
What you need to measure?
Will you compare? If yes, whats the clinically significant difference?
How you will collect the data?
Check the proper study design: https://www.equator-network.org/
Count things in people: STROBE
Identify potential risk factors: STROBE
Compare two or more interventions: CONSORT
Test a diagnostic device: STARD
Test something in vitro
J. Krithikadatta, V. Gopikrishna, M. Datta, CRIS Guidelines (Checklist for Reporting In-vitro Studies): A concept note on the need for standardized guidelines for improving quality and transparency in reporting in-vitro studies in experimental dental research, J. Conserv. Dent. 17 (2014) 301–304.
C.M. Faggion Jr, Guidelines for reporting pre-clinical in vitro studies on dental materials, J. Evid. Based. Dent. Pract. 12 (2012) 182–189.
Explore feelings, experiences and other things in persons