Basics
Build Order
Footmen Build Order:
Send 3 workers into the goldmine, build an Altar with the fourth, a Farm with the fifth. The 6th worker builds a barracks. The worker who built the first farm builds a second one right after the first is done. After that build as you like - Tech to tier 2 as early as possible. Overall you should have 5 workers in gold, 6 in lumber and 2 more which will build (or gather lumber when idle).
Alternately, you can keep the 3 on gold and 1 building two farms in a row, and devote one person to build a barracks, then afterwards an altar. This has the drawbacks of making you a bit more vulnerable to hero harass, and not letting your hero creep solo if there are very easy camps on the current map. The advantages are that an overall army of 5 footmen and a hero is finished faster (because 5 footmen take longer than a hero, and you're making the barracks first), and you'll have more resources because more peasants are going straight to gathering early on. If you're good at managing militia, this is one of the most solid starts in the game, and can easily branch off to rush, cc, or defense.
or you can make 3 out of the 5 peasants build a Farm, an Altar, and a Barracks and have them go to wood immediately afterwards before pumping out five Footmen and an Archmage fast while two more Peasants are directed into gold while the other two from the five you had go into gold then go creep.
Against Human
Archmage first, build as many Spellbreakers as possible and add a few Priests. Second hero MK. Since the enemy probably builds the same units your best chances to win are either better micro, higher hero levels, a lucky creepjack or a perfectly timed attack on the base, when you know that the enemy is not there. If an expansion is possible to build and hold long enough that you actually make profit from it, then build it.
For lvl 20 follow this instructions!
For higher lvl, play Am with some footies, t2 add mk and one arcaine sanctuary. On your way to t3 you add a workshop ( blacksmith needed ) and built some mortars against the enemy casters. Your army should consist of some Priests for inner fire, some mortars to kill the enemy casters and knights! Of course you can add a Paladin when you are at t3. Yo can use the mortar teams to scout your enemy and check out if he is trying to get mass air, if he tries so, you can make an expansion or attack him because of your advantage. If this doesn't work make Dragonhawks as air conter.
Very important in hu vs hu is very good micro in the early game. When you fight with Am, we`s and footies vs your enemy with the same army,it all belongs in your micro. The winner of the first fights is probably able to tech faster and that's what's really important in this matchup!
Against Orc
Archmage first with footies. Build an early blacksmith(while teching on t2). Build rifleman and a few Sorceresses( 3-4) and add a few Priests. Buy a Beastmaster from the tavern as second hero and try to win through the summons, start an attack to the burrows. Try to level your heroes as much as possible and attack before the enemy TC reaches level 3 or the Farseer reaches level l4. Because if that happens his Shockwave/Chainlightning will kill your Sorceresses and Priests in no time(Healscrolls solve) . Only build an expansion if you are 100% certain that you can hold it (Lost Temple), else it delays you too much which gives the orc time to level his heroes.
Alternatively you can pick the Mountain King as second hero and skill bolt. if you have enough rifleman and maybe sorcs, you should be able to focuss single units.
Against Night Elf
You use Archmage as standard hero. At first you build footies, cause most night elves will produce archer. The footies make extra damage to the archer, so they are best but you have to micro them, the attack damage of the archer is not bad at all. If the NE goes huntz in the early game, you have to switch to rifles soon. A blacksmith, necessary for rifles, should be build anyways. The second hero can be the mk, with bolt and more important clap, he can slow enemy units, and then the archmage can use blizzard, which can be retrained. But clap is good anyway, because it slows the enemy attack. The T2 units at the human should be mass caster and then breaker or rifles...
Another tactic can be knights and mortar... You build same heroes and this special units, instead of rifles and only a few caster or even no caster... Early game is the same...
Against Undead
Archmage first, build a few footies for easier creeping and tech to tier 2 ASAP. Build mass riflemen, a few priests and maybe 1 or 2 sorcs with slow autocast set to off. The undead will most likely play mass destroyer, so sorcs will be useless any way, but there may be some situation where a manually casted slow will allow you a hero kill, or where invisible will save your hero. Try not to force the win through an attack on the base - undead bases are strong. Also don't fight if the destroyers have mana. Try to win through a fight in which destroyers have no mana, so your riflemen should rip them apart. If the enemy is attacking your base, let him waste all his mana on buildings which you should mass repair. In some situations an expansion is possible even before the enemy has destroyer. If you manage to do that, and if you manage to hold your expansion against the destroyer attack, you will soon have a huge army of riflemen, which will make things a sure win.