The key things to master in terms of being able to see anything with a direct ophthalmoscope are:
1) Having a dark room
2) Having your eye close enough to the ophthalmoscope
3) Having the ophthalmoscope close enough to the patient
4) Having the ophthalmoscope properly focused
5) Having you, the ophthalmoscope, and patient properly lined up
Some people find the Welch Allyn PanOptic ophthalmoscope to be easier to use than the traditional type. The downside to learning on one of those is that you might not always have access to one.