I am still working on my instrument rating and getting closer to being ready each month.   My regular instructor had to miss a lesson so I went into the RedBird FMX full motion sim with another instructor.  Instead of the usual local airport approaches we went with KCMI and I did ILS and GPS approaches.   One mistake that I made was not briefing the GPS approach after having briefed and done the ILS.  As a result I was not familiar enough and had not thought it through so I made several mistakes in shooting it.  One glaring mistake was I kept looking up for a glide slope indication, not seeing it and as a result coming in way too high.  I had to use an excessive rate of descent (can you say vomit comet?) which would have been a big fail with both the FAA and any passenger with me.  As usual every lesson is a learning experience for me.  I do see that not regularly shooting each type of approach will likely cause you to potentially do something dangerous at a bad moment.  I will do better next time.