Wisp Detonate
If you're not regularly using Detonate, you're not using the Night Elves like an advanced player. There are many uses for Detonate throughout the game. When the enemy Hero rushes, bring some Wisps and Detonate on their Heroes. If the enemy Heroes are using summoned units, use Detonate on them. Take some Wisps and have them follow your Hero around. When you meet the enemy, use them to Detonate on the enemy. If the enemy has a lot of spellcasters, use Detonate to get rid of their mana. Try to sneak up on them during combat. Send some Wisps to your allies in team games so the Wisps will be near the battle if your ally is attacked. Make sure you learn to use the Hot Key as this makes it 90% easier to use Detonate. If you need Detonate in battle right-click your Tree of Life on your Hero and queue up a bunch of Wisps. Learn more.

Detonate Counters: Run from the Wisps. Many Night Elf players that use Detonate aren't very good at it. So you can often run out of the way and they will destroy themselves and miss. You can also use instant kill spells such as Chain Lightning or Forked Lightning. You can also focus fire on them with ranged units.

[ Click to Enlarge - 194 KB ] A Night Elf player tugs some Wisps around to use on enemy Summonables such as Water Elementals and to remove Mana from casters.	[ Click to Enlarge - 142 KB ] A Night Elf players Detonates on some Water Elementals and an Archmage.

Using your Ancients for Defense
Ancients can attack while rooted. When you uproot, their armor drops from Fortified Building armor to Heavy armor making them much weaker. However, your Ancients actually take less damage from siege attacks when uprooted, so if your enemy is attacking primarily or exclusively with siege weaponry (as in the case of mass siege engines, for example), uprooting them can actually help them survive. If attacked try to root as soon as possible. Since Ancients can attack while rooted, and it's not wise to move them during combat, it's best to build them in such a way that the Ancients are close to each other and can back each other up. You can build your town so that they are near each other or placed in such a way that they are ideally located. Always try to fight near your Ancients when someone attacks your town for additional base defense. Ancients cannot attack while producing a unit, researching, or upgrading. You will have to stop those operations if you want to have the Ancients attack.

When your town is under attack and there are enemy units around your Ancients, cancel building units so that the Ancients will attack the enemy. Use Wisps to repair the Ancients. As the enemy backs away from the Ancients, then start using them for training. You can also start building additional Ancients in a safe area so that you can use them to train while the other Ancients fight.

Use Map Terrain For Defense
If there is a ramp leading into your town such as on Wetlands or Market Square, build on the ramp. Then if players try to attack your town they will have a difficult time getting to your Tree of Life.

[ Click to Enlarge - 162 KB ] On Wetlands a Night Elf player blocks their ramp with Ancients of War and Huntresses. The Huntresses can be placed on Hide (especially with a Moon Stone) so that the enemy doesn't even know why they can't get up the ramp. The Ancients of War also can defend the ramp and Wisps can repair from the other side. In this case the two enemies were driven back from this setup and were forced to retreat (funny). You can even use Ancient Protectors and Glaive Throwers on the other side for defense. This makes it very difficult for the enemy to get into the town. Nature's Blessing can further enhance this setup. There is still room for units to pass through and get out of the town though. There are even Moon Wells to heal the units defending.

Fast Expand
The Night Elves, along with the Humans have the capability of fast expanding. Build a Tree of Life while you're attacking the Creeps.

Build a Tree of Life away from a Mine before the Creeps have been cleared. Once the Tree of Life is completed use it to fight the enemy Creeps there. Have to repair it using Wisps. The Tree of Life is often capable of clearing an expansion without too much help, depending on what Creeps are guarding it.

[ Click to Enlarge - 142 KB ] A top Night Elf player is fast expanding using only 3 Huntresses and a Hero.

Hiding Expansions
Using Eat Tree you can clear room for a Tree of Life hidden in the trees while still able to reach the Gold Mine. You may find this useful when you're trying to hide an Expansion.

[ Click to Enlarge - 182 KB ] A player cleared some room for the Tree of Life using eat Tree. During this FFA game everyone walked by this mine and didn't even notice the player's expansion because of his hiding spot.

Tree of Eternity
After your main Gold Mine is used up you can/should research Nature's Blessing (if you haven't already) and walk your Tree of Eternity to a new Gold Mine. Be sure you have a Town Portal Scroll (and continue to buy them) so you can Teleport to the Tree of Eternity and save it.

[ Click to Enlarge - 182 KB ] This Tree of Eternity walked to a new Gold Mine.

Hide Fun
Hide can be used to create invisible walls. This can be used to block off choke points such as Ramps or spaces into your town in between the buildings.

[ Click to Enlarge - 143 KB ] On The Crucible a Night Elf player uses Hide to create an invisible wall of Archers and a Priestess of the Moon. Confused, 3 enemy armies bounce up against the invisible wall unable to exit the base. The 2 other teammates attack the enemy town while this Night Elf player is "blocking". The enemy team could have simply cast Blizzard or used any skill that can Detect Invisibility.

Seeding
When you notice that your opponent isn't scouting around his base, you can easily build an Ancient of War nearby and start pumping out some units (Glaive Thrower works best). When you go to attack, bring those units and the Ancient(s) into your opponent's base, and keep building units as you attack. Be aware of units attacking the Ancient of War and your newly produced units (although they are foolish to do so, as it takes their units away from attacking your Glaive Throwers).

One can also build Ancient Protectors inside your opponent's base while raiding, if you follow this up with an Ancient of War, you can build your whole army right in their base (perform with extreme caution). This strategy works well against Night Elves (due to their delay in getting defenses), marginally against Orcs, but don't even try it against Humans or Undead (due early towers and to Militia or lumbering Ghoul and Blight Regeneration respectively).