So what do you umans tink weel be talkinz about 'ere? Well we could talk about da squig beer and blastin da gitz but letz talk about winnin.
Well here we go. There are several parts of the ork army and you should need to know them all to play effectively. The first part are the boyz. These are you mobs of ork warriors and gretchin screeners. They are you close combat muscle and you should keep the orks behind a screen of grechin to protect them. These close combat orks should be a deadly opponent in combat. Especially if they are Bad Moons which may take high powered weapons. The grechin should be armed with some lonbg ranged ordinance to shoot with. This contingent of your army should advance in the center of the battlezone to enguage the enemy as fast as possible.
The second is da speedos. These are warbikes, buggies, and wartraks and scorchas. They are best used in massed squadrons in which they can easily combine their firepower to wipe out almost any opponent. These are best used to sweep around one flank and hit your opponent from the rear and take out his heavy weapons troops whic would otherwise shoot up your precious boyz mobs. Even if your speedos don't kill the heavy weapons troops, then your opponent will have to do something about them, taking the heat off your mobs. Speaking of heavy weapons that brings me to my next point.
Da shooty stuff. Basically anything with a heavy weapon goes in this category with one majour exception. Dreddies can go into this or the troops category. They can support your boyz squads with power claws or you can equip them with 4 heavy weapons and make them into firepower laden monsters. Nobs with heavy weapons and mekboyz with shokk attack guns are a great part of this section of your army, as are deathskull lootas with kustom kombi weapons. Obviously you use these to shoot up your enemies(duh!).
Using these tactics are a great starting point for your own ideas, and if they alone win you a game or two then great, but you WILL have to change them eventually to accomodate for you opponent getting wise to them.
Thanks for staying with my rambling through all this, and may the dice fall well to you.