IF IN DOUBT ASK

a must on all drawings, the user should assume nothing.
 

DO NOT SCALE PRINT

people do and always will scale from prints, but paper will stretch and shrink depending on its quality and storage/usage environment so the user must treat any such scaling of non dimensioned areas of a drawing print as nominal only. 
 

1st ANGLE PROJECTION

3rd ANGLE PROJECTION

the projection style used should be noted on the drawing, along with a small diagrammatic representation, to avoid any confusion.
 

SCALE 1 : __

in CAD you should always work at 1:1 with the 'model' but have to apply a suitable scale to allow paper printing of those larger items like ships and office blocks, also, for example, something drawn at a scale of 1:100 on an A1 sheet will scale 1:200 when printed on an A3 sheet, as an A3 sheet is truly half of an A1 sheet, so this should also be noted on the drawing if prints are to be produced on two different sheet sizes. 
 

ORIGINAL SHEET SIZE : Ax

very important in CAD if you scale down the complete drawing to print out on a smaller sheet than the original.
 

ALL xxx  IN xxx
UNLESS STATED OTHERWISE

a useful note which covers many applications and will save a lot of identification problems on large or particularly busy drawings.
ie. all dimensions in millimetres... , all pipework 2" ... , all wiring .75mm ..., all surfaces finished 3.2 ... etc, etc.
 

REMOVE ALL SHARP EDGES

obvious enough, but very important for anything going to be handled in/during production or after completion.
 

DEPTH OF PAINT FINISH MUST BE MAINTAINED ON ALL FACES, INCLUDING CORNERS 

a useful covering note especially if an expensive paint finish is specified, for high profile presentation or perhaps use in particularly arduous conditions, as corners are not always as well coated as flat areas and are often heavily used, eg. door edges.
 

UNMARKED TOLERANCES __

in theory it is not possible to manufacture anything without accepting a level of tolerance in the production, but it can make a drawing very fussy and perhaps a little overpowering if every dimension has an individual tolerance, especially if it doesn't really matter that much, so a general note is useful to cover all un-toleranced dimensions.
ie. up to 300mm   ± 0.5
     300-1000mm   ± 1.0
     over 1000mm  ± 1.5
     angular           ± 0.5º  
              or as appropriate to your own industry.