Click illustration above for animation and production instructions from Tools for Clear Speech By Baruch College.  While the animation only shows /o/, the audio pronounces this sound the way it is usually spoken in mainstream American English, as a diphthong /oʊ/, so to complete the diphthong, you can either click on the /ʊ/ symbol or the /u/ symbol on this page, as the latter portion of this diphthong lies somewhere between the two. You can also visit the Sounds American website for animation of the diphthong, which you can find by clicking the /oʊ/ symbol on their site.