The quotation "Why not spend some time determining what is worthwhile
for us, and then go after that" is attributed to William Ross.  My
question is, who is this William Ross (needless to say there are many
famous people of that name) and when and where did he live?  I require
an answer of only one or two sentences, but I do need the source of
the information.

Hello.

The quotation is almost certainly from British philosopher William
Ross (1877-1971).  He was born in Scotland. He was a professor,
provost and vice-chancellor at Oxford.  He wrote several books on
philosophy and ethics.

There's a brief biography at britannica.com:
http://concise.britannica.com/ebc/article?eu=402513


Several books were instrumental in helping me to identifying William
Ross (1877-1971) as the author of the quotation.

First of all, the "Why not spend some time determining.." quotation
appears on Page 17 of the book "Solutioning.: Solution-Focused
Intervention for Counselors."  A citation (and bibliography) indicates
that the quotation is taken from Page 9 of:
Peter, L. J. (1977). Peter's quotations. Ideas for our time. New York: Morrow.

A different quotation from William Ross appears on Page 30 of
"Solutioning."  That quotation is also cited to Peter's quotations.

Thus, it became clear to me that "William Ross" is known for more than
one quotation and is probably quoted widely.   I then searched
Amazon.com for "william ross", "quotation."  This search led me to a
different William Ross quotation (also about spending time reflecting
upon priorities) on page 124 of the book.  Plato, Not Prozac!
http://www.amazon.com/exec/obidos/tg/detail/-/0060931361/

I then searched for "william ross" within this book and found the
following on page 286:

"William Ross, 1877-1971
British Philosopher
...
Ross points out that duties come into conflict, in the sense that we
often have to fulfill one obligation at the expense of another. His
theory suggests that we must prioritize our duties carefully,
according to each situation"
page 286

Plato, Not Prozac! : Applying Eternal Wisdom to Everyday Problems
http://www.amazon.com/exec/obidos/tg/detail/-/0060931361/

Thus, the theory mentioned here is almost identical to the sentiment
of the "spend some time determining what is worthwhile" quotation.  As
such, this must be the "William Ross" that you're seeking.

-------

search strategy:
amazon.com: "some time determining", "william ross", quotation
google: william ross, philosopher 1877

I hope this helps.

Great reference work!  Thanks very much.