I'm preparing to take the General-Class license exam at the next opportunity. It took me about a day of thorough study without much else going on to get to the point where I hope to pass it.
Study has been with Ham Test Prep by Iversoft, and Dan KB6NU's No-Nonsense Study Guide. The Ham Test Prep app for Android got me to about 75% right, and it was reading Dan's uncomplicated writing that pushed me toward figuring out the ones that I didn't know or couldn't memorize.
The one piece I don't understand (yet) is Ohm's Law, which shouldn't be that hard (but there it is). It took a while to get the right stuff burned into my brain about components in series vs components in parallel.