Some basic strategies for each race:
Night Elf:
VS UD- The UD will do one of two things... Either he will go Death Knight first and mass ghouls, gargoyles, and statues, or he will go Death Knight first and mass fiends and statues.
Against either, you can do the same thing. That is, use a tavern build (I recomend thumbing down non-tavern maps if you play as NE, it is their best bet for winning) and mass archers and huntresses. An Example of a "tavern/nuetral hero" build:
4 starting wisps to gold, 1 to lumber
1st queued wisp to build moonwell, rally it to build Alter
2nd queued wisp builds first Ancient of War (AOW)
3rd wisp to lumber
4th to gold
5th to scout for enemy position
6th and 7th to lumber
Right as your 1st moonwell finishes (and that wisp goes to make an alter), pull a wisp off of lumber and build a 2nd moonwell
Rally your AOW to the nearest tavern
Build a 3rd moonwell when the 2nd completes
When your alter is finished, buy a Pandaren Brewmaster hero (Drunken Haze 1st skill)
His skills per level 1 Haze 2 Fire 3 Fire 4 Haze 5 Fire 6 Ultimate 7+ your preference...
Continue making archers (rally them to hero) and make a 2nd AOW and a Huntress Hall when you have the resources. Level your hero up as quickly as possible as you make more archers and hunts. At the 1st daybreak, you should but a scroll of protection and scroll of healing from the Goblin Merchant, and then immediately attack your enemy.
This is the only point in the entire match in which the UD will be weak... And this is when you must kill him, or you're in for a very difficult game.
Focus on killing Ziggrauts 1st, and do as much damage as possible before the enemy teleports in (move army back a bit when you see the TP light), then cast Haze and Breath of Fire on the ghould or Fiends and try to kill them as quickly as possible. Ignore the DK, he is practically invincible. Don't forget to use scrolls when necessary... And keep the Panda kind of on the outskirts of battle casting his spells, so that he can run easier when the DK and Lich try and kill him.
Upgrade your Tree of Life during this battle, and Teleport out if your army is weak. If you lose this battle, get an expansion up, and then creep some more until you can get Druids of the Talon. Don't bother with a 2nd hero in this match-up; the UD heroes are far too exceptional at hero killing, and any level 1 hero is just going to die right out of the alter.
Try to upgrade your tree again soon, and start massing hippogryphs and Chimeras. Buy a Staff of Preservation from the NE shop, so that you can save your Chimeras as they near death. Attack again when you have a good army of chims and hippos... Good luck.
VS HU:
This will be a slightly easier match-up than the last one. You have three options of what to do (I always choose the 1st, but you may be different):
1. Use the tavern build from earlier, only get a Tinker and fast creep to level 3. As soon as you hit that mark, attack the Hu base and kill as many peasants as possible.
Tinker skills- Level 1 Factory 2 Engineering 3 factory 4 Engineering 5 Factory 6 Ultimate
Don't get too many archers in this match-up (defend makes them obsolete fast), go mainly hunts (with attack upgrades). And get goblin merc priest if pssoible (they can abolish water ellementals). You should be able to continually attack and pressure the HU base until he dies. If the HU keeps driving you back, and hass a lot of casters and a Mountain KIng, then it is time for you to start adding dryads to your army. Makesure to research abolish magic ASAP for the water ellementals.
2. Another option for this match is to make a Demon Hunter (DH) as your first hero, and continually use immolation on enemy peasants all throughout the begining of the game. Mass huntresses and win...
3. Last option, and the one most NE players still use I believe (and the one HU players have learned to beat easily): Make a DH as your 1st hero, with mana burn as first skill. Harass the enemy Archmage all game long, mana burning him. Upgrade yor Tree of life without making any archers or hunts (hire mercs later if necessary), and build a huntress hall. Make two Ancients of Lore when you've finished, and start dryad/bear production. Tech to tier 3 (upgrade tree again), and research the master bear upgrade. Mass bears and dryads for the rest of the game.
VS Orc: Use the Tavern build as before, and get a Beast Master (1 quill beast 2 hawk 3 hawk 4 beast). Only build one AOW this game, and tech to tier 2 (build huntress hall while teching). As soon as you reach tier 2, build one Ancient of Wind and one Ancient of Lore. Mass archers, druids of the talon, and dryads (with abolish). Get a Firelord as your second hero, and attack enemy when your army is large enough.
Tech to tier 3 eventually, and start making a few chimeras (with defense upgrade so that it takes multiple bats to kill).
Win.
VS NE:
Three options here too... The first being the easiest, the last being what I use:
1. Make a Prietess of the Moon as your first hero, and mass hunts. Add in a couple glaive throwers and then attack your enemy. Do this all game long, continually keeping on the pressure...
2nd option: Nearly identical to the 3rd option VS HU, only you will tech a bit later here and make a single AOW. Harass enemy hero early game with mana burn (as used against HU), and make a few archers. Later, mass drydas, bears, and a few MGS. Get a Naga or Panda (I prefer panda if enemy doesnt have dryads yet) as 2nd hero.
The reason you tech later here, is because a lot of NE players go with "option 1" and mass hunts, and you will need the archers (and a lot of micro) to fight them off until you get dryads.
Option 3: The hardest to pull of, but when perfected, gives you a more dynamic game where you can counter your enemy easily.
Go with the tavern build order, and make a Tinker... Fast creep.
If your enemy harasses you with a DH, he is teching... You need to do a one AOW tech too. Do not defend your base with the Tinker when your enemy harasses it! Keep fast creeping; and build your base so that the moonwells are protecting wisps, and the AOW is protecting the wells. You can have your Tinker to level 3 (!) by the time your level 1 emeny hero gives up on base harassing (I can show you replay proof). When you get to teir 2, get a Panda and mass hippo riders. Your enemy, who will be going bears dryads, will be weak against this. Just be sure to focus on the dryds with the hippos 1st, then go to bears.
If instead of a DH, your enemy harasses with a Priestess, he is going option one, and you need to go 2 AOWs and mass archers and hunts. Add glaives to the mix, and tech semi early. Get a panda at tier 2.
Thats it for "basic NE..." (other races soon).