If I had my life to live over, I would try to make more mistakes next time. I would relax. I would limber up. I would be sillier than I have been this trip. I know of very few things I would take seriously. I would be crazier. I would be less hygienic. I would take more chances. I would take more trips. I would climb more mountains and swim more rivers. I would burn up more gasoline. I would eat more ice cream and less bran. I would have more actual troubles and fewer imaginary ones.

Don Herold (1889-1966) American humorist, cartoonist, author

Essay (1931-12), “I’d Pick More Daisies,” College Humor magazine, Vol. 10, No. 96
    (Source)

Also attributed to Nadine Stair, and a Brother Jerome, among others. This essay has gone through a variety of revisions and homages, both by Herold and by a variety of borrowers. The earliest reference I could find was that cited here, as quoted in The Journal of Health and Physical Education (1935-05) [linked above].

The usual citation is to a revised version of the essay by Herold in "If I Had My Life Over -- I'd Pick More Daisies," Reader's Digest (1953-10) (and reprinted in Reader's Digest's How to Live with Life (1965).

Benjamin Rossen, "Who Would Pick More Daisies; A study of Plagiarism and Foolery on the Internet" (2000) wrote extensively on the variations and misappropriations of the poem (though he did not know of the 1935 version).See also: Essay Origin: I Would Pick More Daisies – Quote Investigator®, which includes a nice thank-you to WIST regarding this quotation. The page includes further research into and examples of the various versions of this quote, but concurs on the December 1921 original date. Interestingly, it is likely the actual publication date (not the date on the magazine) was in October, as at least one newspaper article dated 3 November 1921 references it.