The word improcerous means 'low' or 'short in stature'. How is it pronounced?
As Andrew Leach mentioned, this word is currently obsolete. However, as Peter Shor mentioned, we do have records in dictionaries that hint at how it used to be pronounced when it was used. The etymology can also provide some clues.
The Oxford English Dictionary (OED) says the stress is on the third syllable. This word has the negative prefix in-: if we remove that, we get the word procerous, for which the OED does list a full pronunciation: /prəʊˈsɪərəs/. Based on this, I would say the pronunciation of improcerous would be /ɪmprəʊˈsɪərəs/.
This stress pattern seems to be inherited from the Latin word prōcērus. In Latin, a "heavy" second-to-last syllable (one that ended in a consonant or had a long vowel, like ē) received the main stress in a word.
The above pronunciation is only my best guess. You can't always predict the actual pronunciation of a word using the etymology. For example, the OED indicates that the related word procerus (used to refer to a muscle of the nose) is pronounced nowadays like /prəʊˈsɛrəs/, with a short stressed vowel in the second-to-last syllable for some mysterious reason. Also, there is often variability between speakers in the pronunciation of these obscure Latinate words. Merriam-Webster gives the pronunciation I would expect for procerus, /prəʊˈsɪərəs/.