Why is that most/many of our prayers appear to be plural/National requests - shemoneh esreh-barech a leinu, shema koleinu etc. many yehi ratzon’s say “hashem elokeinu ve’lokei ovoseinu - where other prayers take on a more singular/personal requests like we find in morning Bracha “she’asa li Kol tzorki” or the yehi razton that follows there which is “hashem elokai ve’lokay ovosay”? What’s the formula to decide which is plural which is singular?
Your question can really be divided into two - brachos and tefilos (requests). In regards to brachos ("she'asa li kol tzorchi"), unless they were established to be said on behalf of the public/congregation they are always in singular. In regards to tefilos, anything said to be undo a decree is said in plural, to use the power of the group (see tos' in rosh hashana 15a), as well as the tefilos which were established to be said behalf of the public/congregation, and the rest can be either, and it just depends on what it was written for.