Started reading Practical Vim and I’m going to start listing tips I should be using more frequently in VIM.

zz                  redraw screen with current line in middle 
CTRL-o              execute one command, return to Insert mode
CTRL-r {register}   paste from register while in Insert mode 
CTRL-r=             use the expression register to evaluate and 
                    insert a calculation           
q:                  command-line window