PBLANK!
Now I remember an excellent, excellent manual that most of the brits here surely know well.
Trevor Thom's Private Pilot Manual has a volume on Instrument Flying and Radio Navigation. It explais it all with lots of graphs.
The best way to use the HSI and RMI is to turn the instrument into a map, like a "mental ND". You can do that if you ignore the little airplane in the middle of the EHSI and think of your airplane as being in the tail of the needle.
Then you have your situation in relation not only with the navaid but with anything else around it (rwy or whatever).
the boeing document I mentioned recommended the same technique