Secondary professions for an Assassin

Assassins are highly aggressive, focused, damage dealers, better for hit and run skirmishes then drawn out tanking or back-line sieges.

Always remember, when choosing secondary skills, that native skills often have better synergy with the profession's purpose, interact better with the profession's other skills, and benefit from runes.

Assassin/Warrior

 * Assassins do not have any attack speed enhancing skills (Excluding the PvE/Nightfall-only Critical Agility). Flurry, and Tiger Stance can increase the rate they can pull off an attack chain, as well as increase their overall DPS.
 * Wild Blow to cancel important stances.

Assassin/Ranger

 * Barrage damage can be improved with high critical strikes attributes, adding bonus damage to attacks, energy bonus, and effects from skills like Critical Eye, if you use Barrage with Sharpen Daggers, you can spread bleeding in mobs.

Assassin/Monk

 * Assassins can use some Monk Protection skills such as Mending Touch in order to remove conditions from themselves.

Assassin/Necromancer

 * Hex spells, particularly from the Curses line (Parasitic Bond), can be used to drive many attack chains involving the foe being hexed. Although, many primary Assassin Skills, most notably Siphon Speed, can serve the same purpose.

Assassin/Mesmer

 * Arcane Echo can be used to chain Shadow Form when running or soloing.

Assassin/Elementalist

 * The Conjure Spells (Conjure Flame, Conjure Lightning, Conjure Frost) can increase the overall DPS of an assassin.

Assassin/Ritualist

 * Sparing use of weapon spells such as Warmonger's Weapon can aid an Assassin in battle, although weapon spamming is best left to Ritualist primaries.

Assassin/Paragon

 * Assassins and Paragon Skills have very little Synergy. However, you can spam the skill "Go for the Eyes!" in order to increase the chance you get a critical hit, for no energy cost at all.

Assassin/Dervish

 * Assassin and Dervish Skills have very little Synergy.