If the enemy has only 1 to 3 SA units, send in ur ashigarus to let him waste his arrows on them. After they run out then send in your YS. While lining up ur own SA along the river shore. Engage ur YS with his bridge defender while raining arrows donw on them. This is for early in the game when the armies are relativley small. If this doesnt work, then line up ur SA and fire into his YS that r blocking the Bridge. If they retreat, send in ur Daimyo and run him across the shore, 2 to 3 units should start chasing him. Then cross all ur tropps, while using ur SA for cover fire. I find that running the Daimyo along the river shore works early in the game.