It really is one of those things you learn in time...when I look back at my early vids I laugh at how bad the angles are...
The most importing thing when it comes to filming is (usually) lighting...I would recommend getting a 300w-500w worklight (like this:
https://www.bunnings.com.au/arlec-500w-portable-halogen-worklight_p7070598). They are cheap and get the job done...though be warned...they get VERY hot!
2nd most important thing (in my opinion) is angles...I was filming for a long time without using a tripod and it is a LOT harder to get good angles this was...flexible tripods such like Joby Gorillapod
are FANTASTIC...and I would HIGHLY advise investing in one (or a cheap knock-off equivalent).
Frame-rate can also play a very important roll when it comes to filming fingerboarding...so a 'decent' video camera is also needed if you want to avoid ''blurring''...though good lighting will also reduce ''blurring''.
Other than that, all you can really do is practice...either that or take a photography class or something...
Hope that helps out a bit anyways.
- Jono