Blender has a thing called “Grease Pencil” (GP) and it’s extremely helpful when it comes to detailing your mesh. While modelling you can draw anywhere on the viewport by holding down “D” on the keyboard. To erase simply use your right mouse button while “D” is pressed down. My setup is a little different (D + Shift + Left Mouse to erase).
If you have a hard time visualizing flows then GP can help you by drawing the loop and it stays on the screen while you’re redirecting the flow, which brings me to the L-Flow and Spin Edge. In general, at the corner of the L you have two choices, two edges, to choose from when deciding to use the Spin Edge—always remember that.
GP helps me to visualize the look of this creature with teeth. Funny that I have been trying to figure out why he looks friendly when my goal is to make him look angry/scary… looks like the teeth are missing!