First, the NEXT_HOP must be reachable — an unreachable next hop removes a path from contention entirely. Then BGP walks the tie-breakers in order and stops at the first that decides: Weight (highest, Cisco-local) → Local Preference (highest, AS-wide) → locally originated (network/aggregate over received) → shortest AS_PATH → lowest ORIGIN (IGP < EGP < incomplete) → lowest MED → eBGP over iBGP → lowest IGP metric to the next hop → then the tie-breakers: oldest eBGP route, lowest router-ID, lowest cluster-list length, lowest neighbour address.

The first four steps are where almost all deliberate engineering happens. WEIGHT influences only the local router's own choice. LOCAL_PREF is the standard tool for choosing your AS's exit for a destination — set it inbound and it steers outbound traffic. AS_PATH prepend is how you make one of your own prefixes less attractive from outside, steering inbound traffic. MED is a softer, non-transitive hint to a single neighbour. Everything below MED is usually a tie-breaker you observe rather than set.