Florence-based American artist Marc Dalessio has produced a series of short videos, each one making a single point about academic methods for painting the landscape and the figure.
(Direct link to video) This one shows how to use the the sight-size method for landscape.
(Video link) A pocket mirror helps check the accuracy of a portrait. You can hold it both horizontally and vertically to help spot errors in the drawing.
Some of Marc's other one minute videos:
Using a cuttlebone for to prepare the surface of a painting
Scraping down between painting sessions
Sealing gessoed panels
Marc Dalessio's blog
Lines and Colors profile
Thanks, Thomas Kitts