Once your Assassin reaches level 75 or so (perhaps with a help of a leveling build), you will be in a prime position to respec and pick your endgame Build. Keep in mind that your Build will not only define your skills going forward, but also your optimal weapons and armor.
Below you can find some of the best Assassin builds for Diablo 2.
Lightning Sentry (Trapsin)
The Lightning Sentry Assassin — the most common Trapsin build — is the most iconic Assassin build, and dominates the class’s metagame with its potent Lightning Sentry + Death Sentry combination. This build exemplifies all of the Assassin’s advantages — dealing massive damage, from far away, with almost no danger to your character.
A variant on the Trapsin build with a surprising Skill at its base: the infamous Level 1 Fire Blast. At its maximum level, with both Lightning and Fire damage Skills as its synergies, this Skill deals massive AoE damage and bypasses immunities on higher difficulties. It is most popular for use in The Secret Cow Level farming.