Fly the GS intercept altitude until intercepting the GS, crosschecking your altitude against the approachplate. I.E. on this approach:
http://204.108.4.16/d-tpp/1004/00924IL35.PDF (ILS35 to KLAW) if you are on the correct GS beam, your altitude should read 2298ft when passing the OM.
An instructor I flew with a couple of times during primary flight training had experienced false glideslopes once when descending ONTO the GS instead of intercepting it from the GS intercept altitude. He was waaaaay above the 2298ft when passing the OM on the above mentioned approach.
(To explain excactly what I mean... the small font numbers close to the FAF-symbol is the altitude of the point where the GS intersects the FAF DME and/or OM
Other considerations?