Orange is one if not the most powerfull faction having powerfull heroes with strong AOE damage along with the highest spawn of the map. The downside is that it first have to defeat brown before being able to get him as an ally and go outside of Outland. It will also be surronded by both north and south when it is out of Outland having to fight, sometimes, multiple fronts.
Check Orange events here
Illidan - Will of Kil'Jaeden | Eye of Sargeras | Demonic Riual | Metamorphosis(ult)
My skill preference - Will of Kil'Jaeden > Eye of Sargeras > Demonic Ritual. Notice you should have one level at Demonic Ritual before levelling up the rest of the skills.
Lady Vashj - Forked Lightning | Conjure Water Elemental | Waterpool | Summon Royal Guard(ult)
My skill preference: - Forked Lightning > Waterpool > Conjure Water Elemental
Akama - Shadow Strike | Rejuvenation | Silence(Single-Target) | Reincarnation(ult)
My skill preference: - Shadow Strike | Rejuvenation | Silence(Single-Target)
Elder Akama - Shadow Strike | Rejuvenation | Silence(AOE version) | Banish
My skill preference: - Shadow Strike | Silence(AOE version) | Rejuvenation
Naga Myrmidon - powerfull melee unit.
Draenei Sorcerer - powerfull magic caster unit. Forqued Lightning | Far sight | Faerie Fire
Unique Unit: A'dal - very powerfull support unit. Gift of the Naaru
There is 3 types of the first fight at the brown Outpost:
1) Gather all army at your draenei base and then go in an all out attack to try destroy the outpost. The basic strategy most people use. It is more safe even if you lose the first attack since you can keep a close watch on your heroes.
2) Gather the heroes together at south but keep the army split then attack the base witht he army separeted. Not so different as the first one but with this brown won't be able to AOE all your army at the same time.
3) As soon as the game start rush with all units as fast as possible to the outpost. More risk especially against pro brown but with high reward.
If you destroyed the outpost then you should build some farms to restore your hero hp/mana along with your army. It is not a good idea to attack brown second outpost unprepared as it is stronger than the first. You can use Akama to disable the demonic portals which will decrease brown spawn and disable one of the outpost towers. Your army will be much stronger the longer you wait as your spawn increase much faster than brown.
If you fail in the first attack you should just wait for the timer of the outpost to be destroyed then start doing what is mentioned above. Your army will be heavily damage if you try to take it multiple times as it will be eventually be destroyed by an event anyway.
At this time you probally defeated brown. If not better hurry before the outland portal open. It is better to gather a big army before doing one big push.
Then after portal outland open you will have 5 option of attack.
1) Attacking Jintha'Alor. Should be destroyed as soon as possible as you can get a stronger version of Akama and a powerfull item for Kazzak(brown hero).
2) Attacking Scholomance(if not destroyed alredy). Your first priority. It is easy to destroy and give a new base to brown. Sometimes it will be alredy neutral due to the fall of Lordaeron Capital so its even easier.
3) Attacking Andorhal. Very strong base. If undead is alive and not very damaged from north fight it will very difficult to take it from them but it taken it will be a strong foothold for the entire of north invasion.
4) Attacking Alterac City. If south is still fighting horde and is kinda winning usually they will leave Alterac unprotected. A fast surprise attack will easily destroy the base and will damage south Alliance a lot.
5) Attacking Frostwolf Clan. A strong base but its the closest to your initial invasion point. Hard to take but if horde is fighting south alliance if might be a good opportunity to weaken them.
It is important to try balance the fight between the faction. Destroying either Frostwolf or Alterac for example while they are losing is not always the best idea. Try to strike the strongest faction in the moment before they start fighting you.
At this time most fights are over and you have to deal with the remaining factions. If alliance won in all fronts you are as good as dead. There is no good strategy here. It is a fight between the remaining factions and keeping your heroes alive is the top priority for success. If you have teal as an ally then you have more chances and if he choosed Sunking path it is very important to take Andorhal so he has a good way to go to Quel'Thalas and get his new bases.
Not using Draenei sorcerer in hero group to spawn forked lightning.
Wasting units attacking on brown first outpost when its supposed to fall after some time.
Not using Vashj Royal Guard together with hero group. It has powerfull stats, AOE spell and a very usefull spell to stun heroes.
In the beginning of the game i prefer using the second option of the early game strategy. Brown AOE will dead more damage when all your army is gather in the same place.