My sister has been having visits from the Speech Therapist. They have been very helpful. When my sister's speech started to get a bit slurred she was given some voice exercises to do first thing in the morning to relax the throat muscles which had got tight during the night. This certainly helped.
Things got worse , because swallowing became a problem and she could not get rid of the saliva in her mouth. Now her speech is practically non existent.
One tip which helps. Get the sufferer to speak slowly, and speak if she is speaking to a deaf person. Really shape the words with her mouth. The speech therapist can help with so many problems, swallowing, eating etc - she is your friend - use her. With PSP you have to have help, advice and support from so many - never be afraid to ask and demand.