the worst single thing you can do

Perhaps the worst single thing you can do to spoil your looks is to let your knees spread apart.

Lane, Janet. 1947 . Your Carriage Madam, a Guide to Good Posture. New York. John Wiley and Sons. p.116

if you have no widow's peak

If you have no widow’s peak, you can simulate the effect by parting your hair in the middle and brushing it back like a wing on each side of the part.

Cocks Dorothy. 1935. Help Yourself to Beauty: A Modern Woman's Practical Guide. New York. Harper and Brothers. p. 70

do without

The woman who is overweight should try to walk at least 2 miles a day and do without any unnecessary sleep. 

Garth, Margaret, Wrench Mrs. Stanley. 1922. Home Management, A Comprehensive Guide-Book to the Management of the Household. London. Daily Express Publications. p.706

doing things that thin people do

Start to ‘think thin’ and get in the habit of doing things that thin people do. 
Drake, Debbie. 1961. Debbie Drake's Easy Way to a Perfect Figure and Glowing Health. New Jersey. Prentice-Hall. p.69