In 99 of the games my species has been "random".
My present main tactics are:
First, build an Altar and generate a Hero. I continue with farm unit, then basic unit production unit, then a Town Hall upgrade and further buildings and upgrades. I normally generate additional Heroes as soon as possible.
I always have all my units as Control-Key units. All my heroes move together in control group 1. They are present in all attacks and defences. Wherever there is a skirmish, my heroes move to be present. This is an essential Warcraft 3 tactic employed by nearly all players. Strong heroes win games.
So my tactic is that I move my heroes around the map killing all of the numerous NPCs as quickly as possible. As they progress, they are joined in their skirmishes by increasingly strong units generated by my town and expansions.
I will construct some basic town defences to give me time to get heroes back to base/expansion if such places are attacked. I rarely attack the enemy base until I have largely upgraded and a well equipped army. I roam around, with the heroes, killing NPCs until the enemy attack. Then I repel the attack, further strengthening my heroes.
At some point I will execute a massive attack on the enemies biggest expansion. I wish to destroy their town hall building so Hero's cannot use their Town Hall portal item. I continue destroying their expansion until their forces arrive. When their forces arrive I instruct all units to attack their heroes (using Coil, Novablast, Mana Burn, Shockwave, Storm Hammer, etc all against a single hero until it dies). This way their heroes do not gain from the battle. If their force is strong then I retreat by Town-Portal-Scroll and attack a different expansion as quickly as possible.
When I succeed: Their heroes are weaker than mine, and when their expansions fall they surrender or I finally attack and destroy their main base with both superior numbers and equipment. (Or make more than one attack, pausing to replenish my forces. Without expansions, they cannot match forces more than a few times).
When I fail: They attack my main base with many troops, my heroes die and my numerically inferior defenses are overrun. I attempt to upgrade an expansion to replace my decaying main base but invariably this doesn't work.
When it's close: When they attack, in order to make them leave I attack their main base. Their attack teleports away, and I then cease my attack and immediately attack an expansion (if possible). Such tit-for-tat results in a close game.
When playing against Undead I use air units. When playing against Night Elves I use brute force units. When playing against Human's I use very strong, fewer, units and quick-kill units to prevent their Priests healing units. When playing against Orc's I use "general" units, not too many or too few.
When playing with Undead I don't use enough Necromancers. Some players use many Necromancers and therefore flood battlefields with Undead skeletons. This is effective, I should do it more. When Undead I heavily rely on Heroes, standard units and then flyers. I especially use the Death Knight hero, then the Frost Sheild/Novafrost hero.
When playing with Humans I use Knights and Priests along with Heroes. I rarely use flyers. I especially use the Mage, and then the Dwarf hero.
When playing with Night Elves I use Hunters, archers, and play more defensively than usual until I can back up any main-town offensive with Chimera's. I use the Defender hero (Force of Nature).
With Orc's I generate as many Wyverns as soon as possible and concentrate on upgrading them. I use the Feral Spirit/Chain Lightening hero and then the Stomp/Shockwave hero.
With all species I will, if possible, buy Goblin Sappers and Troll Healer units. With sappers, I send a few skeletons/water elemental/feral spirit units towards enemy base to attract enemy fire, followed closely by sappers that take out key buildings and defenses. I use the Troll Healers in the same way as Human's use Priests.
With magic items I normally try to give all speed upgrades to my slowest hero, give all strength upgrades to the "assasin" hero (eg, the Dwarf with 'Bash') and in general try to generate a very strong Hero (normally this is the first hero I produce) even if it means leaving the other's mild.
I frequently buy scolls - the "heal all nearby friendly units" and the "grant all nearby friendly units +2 armour" scrolls in particular.
My weaknesses: I don't do enough early scouting. I don't use Necromancer enough. I don't attack enemy base (therefore forcing them to purchase defensive buildings) early enough. Sometimes not enough troops in favor of strong heroes (can fall to a mid-game powerful strike).
Strong points: Powerful sudden attack on expansions. Good hit and run tactics with heroes and sappers. Expansions are defended well and made relatively early.
I felt like writing all this up... not that anyone I know plays Warcraft though!