Buses run from various destinations within Yunnan, including a wild overnight sleeper from Kunming (¥109). Some connections, including Jinghong require you to change buses in Mengzi. The bus station is within walking distance of the border post, and Lao Cai is just across the bridge. The border is open 8AM-11PM (7AM-10PM Vietnamese time).
When leaving border office, chinese border officers can have a small paper with brief hekou map and basic glossary available.
Beware of helpful guy speaking English at bus station. He will offer help for selling bus/train tickets in Vietnam for triple their real price or exchange currency several times more expensive than in respectable places. Check prices and exchange rates in advance. Tickets can be bought easily at Vietnam side of border.