I have successfully diagnosed and treated MRSA and upper respiratory infections in myself. I NEVER suggest anybody else to self medicate. Most people do not take it seriously enough or do enough research to self medicate. All that being said, I think it is a shame that we live in a system where it is so expensive and inconvenient to see a real doctor that people resort to this kind of thing.
Gram stain, because it's very fast (minutes) and can tell you, e.g., that you have Gram positive cocci in clusters (thus, likely staphylococcus species).
Culture, then, to grow the bugs and see what nutritional requirements they have and what biochemical modifications they make. Catalase producing? Likely staph aureus.
Finally, sensitivities: resistant to oxacillin? MRSA.
One could imagine PCR-based tests, too, though at my institution such a test is not in use.
Getting back to my question, how did you successfully self-diagnose MRSA?