I once did this:

Started by securing Shinano on the first turn, hiring an ashigaru and a general to protect the province. On the second turn, he used his starting army to take Kozuke and Echigo. Also used his starting monk to convert the Ikko-Ikki rebels in Echigo. He then moved his army to Hitachi and declared war on the Hojo clan. Captured their provinces, defending his own. Once I secured my borders, I focused on developing my provinces and building up my armies.

One of the key units of the Uesugi clan is Yari Ashigaru. They are cheap to recruit and maintain, making them an excellent unit to replenish an army. Another important unit is the cavalry, especially the Uesugi light cavalry. They are fast and can be used to flank the enemy or pursue fleeing units.

To make the most of my clan's unique abilities, I focused on developing sword schools and building Buddhist temples. This increased my melee attack and defense, as well as my clan's overall happiness. Also, the Uesugi clan benefits from increased unit experience, so I try to keep my units alive and well.

Overall, the strength of the Uesugi clan lies in their defensive ability and strong infantry. By defending your borders and rebuilding your provinces, you can weather any storm.