If you want to work with demons, I suggest not using the 4 angel names and sigils at the same time as a demon sigil. For a general guide on evocation techniques Evoking Eternity by EA Koetting is a great book. I also made some posts regarding this subject in this thread, instead of reposting them here.
This is just my own experience ( UPG or whatever ) but I found much better experiences/results and even communication from the demons themselves that they do not prefer to be called simultaneously with 4 Judeo/Christian Angels.
You should also still do a banishing before hand, I highly recommend Protection Magick from BALG for effective banishings.