good job FC, welcome to the fold

Some of tips from my own games - always take an SC with Eldar, they're very fragile and it doesn't take much to make them start missing activations.
Never leave anything unsupported (like your scorpion - I did that once too!).
Guardians + wraithguard are simply evil assaulting out of wraithgates, particularly if you play them with RA saves.
Guardians+wave serpents is a very effective combination, always use the wave serpents to screen the guardians in a firefight.
Take firestorms whenever you can, they are stunningly effective AA (I once took down a thunderhawk filled with marines with one) and not bad at other things - they will restrict your opponent's freedom of movement in the air.
Always take 1 nightspinner battery - they won't last long but are very useful for prepping enemy fms for assault.
Vampire + aspects (4x scorpions - 2 exarchs - and 4x dire avengers is awesome) is very useful, though a very obvious tactic.
Storm serpent + vypers + guardians w/ wraithguard or aspects is a very mobile and effective strike force.
Always try and assault so that the assaulting fm consolidates into support range for another assault.
Never assault unless you're pretty sure you can pound your opponent into dust - prep with BMs, casualties, line up supporting fire, the works

There's more I'm sure, just can't think of anything else just yet!