For an A1 poster use one and a half line spacing. This does not waste space and still gives good text readability. Left alignment is best because if the text is forced to fully justify then it will have too big spaces between the words on some lines as the computer stretches them to fit. 

  • Section headings (Introduction, Methods, and so on): use bold, 60points for an A1 size poster, but a minimum of 40points.
  • Text of an A1 poster should be 30points (with a minimum of 24points) and the recommended font sizes for captions and references is 18points (with a minimum of 12points). 

Be consistent. Choose one font and use it throughout the poster. Add emphasis by using bold, or colour; italics are difficult to read.