According the "THE SUNDAY TIMES BOOK OF DO-IT-YOURSELF" (Published in 1976 by Sphere Books Ltd) the correct ratio of sand to cement for bricklaying mortar is two parts of sand to one part cement.
But only if the cement is already premixed with lime for bricklaying. If not the correct mix for above ground bricklaying is 5:1:1 (sand, cement, lime)
No, that's a vicious lie. A lie I tell you. "One part masonry cement to four of soft sand is suitable for most work, but certain bricks may need a slightly different mix" is correct (to my knowledge). For reference, "the lie" is the correct ratio for pointing work, I believe.
3:1 is a very strong mix and would have very limited workability. (As well as being expensive).The correct mix for above ground work, using a medium density brick would be in the region of 4:1:1 to 6:1:1 (sand:cem:lime). The lime would act as a plasticiser and increase the workability of the mix, as well as retarding the setting time of the cement.