Know sectional charts thoroughly, as well as looking-up locations via Lat/Lon. METARs and TAFs are important as well as weather theory. Practice, practice, practice!
I used the course from Jason Schappert (RemotePilot101.com) since I was familiar with his private pilot training videos. The key thing is to augment
any online course with the appropriate ancillary reading/studying in:
- The Part 101/107 regulations (know the details);
- The Pilot's Handbook of Aeronautical Knowledge, especially the sections on weather and aerodynamics.
Finally, if you use reading glasses for computer work, consider purchasing a cheap second pair that are about 2x-3x your normal strength. The supplement that you are given for reference during the test has details that are much easier to pick up at the right magnification. I usually use 1.25s for computer work and, in addition to those, I brought a pair of 3.50s! This tip came from a fellow "old-fart" who had taken the test and struggled a bit with the supplement.
Best of luck!
Theo