When I make deer-sausage, I use about 2lbs of venison, to 1lb of
el-cheapo fatty pork sausge(breakfast type). I usually by it and freeze it when its on sale. I then add in some additional breakfast sausage seasoning. I guess you could say it's 2/3 less fatty than pork sausage. We like it fine.
For just ground venison, I grind it and just leave it as is, and add trimings to when I cook it if I choose. I usually brown it in drippings or with a few strips of bacon.