Ahhhh! The Trucks...
Like all things ork, take lots of them. You have to give your opponent too much to shoot at. My normal army nowdays has six truck boy squads, three shoota boys and three slugga boys. The slugga boys have a nob with PK and boss pole, and the shoota boys the nob has the big shoota and a big choppa as well as the boss pole. All of them are a full 12 orks (including the nob)
All trucks have red paint, rams, and boarding planks. The extra inch really pays off as you can now move 26" with the turbo boost to get around fast, not to mention the 7" move, a 6" disembark with 2D6 charge really increases your threat range. The rams allow you to go through terrain instead of around it, making for some spectacular sneaky moves to get into your opponents army as fast as possible.
A separate paragraph on the plank is in order. It allows the nob to attack vehicles without the rest of the squad getting out to get shot up. So that land raider full of terminators can get killed, and the boys are not subject to reprisal as the now dismounted terminators have to attack the truck instead of the boys. The great thing I like about the plank is it allows you to attack dreadnoughts without having to loose most of the squad. Not to mention that the dreadnought does not get to fight back. It is a great piece of kit for dealing with those pesky death company dreads. Makes BA players cry and in a few games made them move their DCDs away from my truck boys (using the excuse that they had better targets elsewhere.
Not to mention other things like no overwatch fire from troops inside vehicles, no flechet launchers from tau, etc, etc, etc.
As OD mentioned earlier, you cannot attack with only one squad, you have to combine your attacks, at least two truck boy squads need to attack. I pair them one shoota squad and one choppa squad. the shoota boys will of course declare first so that they suffer the overwatch and this leaves the choppa boys at full strength to do their damage (44 attacks plus nob is a good thing).
Of course there are other things in the army, like a battle wagon full of burna boys, a battle wagon full of tank bustas, a few trios of rockit buggies, and a green baron or even a full squad of coptas (depending on points). All led by a single big mek with KFF and boss pole riding with the burna boys. I don't spend the points on a war boss unless I am running biker nobs, so there is hardly any points spent in the HQ part of my army as it is all in trucks, buggies and battle wagons.
A note on the battle wagon, I have gone to four rockits on each lately, leaving the off the death roller from the tank busta boys wagon as I don't want them in combat, just shooting at stuff. I also give them the red paint as the extra inch always comes in handy. The four rockits make for some semi effective anti air capacity. (The LGS where I play are IA-phobic)
A sneaky but effective tactic for the tank bustas is to move their BW and then dismount the bustas so that their own BW is blocking line of sight so they can shoot at the purifier squad instead of at the rhino.
In one game about a month ago I ran a unit of lootas in the BW instead of the tank bustas (as I knew I was going against a flyer heavy SM army) and it worked rather well clearing the skys of pesky flyers, as well as gunning down a whole squad of DA bikers in one turn. Of course I am still torn between lootas, flash gits, and the tank bustas, so I alternate just to keep things interesting.
As for set up, I always use the football line formation. BW with KFF mek in the quarterback position, a unit of rockit buggies as the center, trucks on either side but within the KFF range. The other BW on a flank, and a squadron of rockit buggies on the other flank in the receiver positions. The green baron usually in reserve or on the far outside edge of the board. This way if I go first, all is well and I am in position to do damage to my opponents army very quickly. If my opponent goes first or steals the initiative, then my army has a bit of protection from the KFF. Then it is off to the races to divide and conquer as fast as possible. A key point to make is to take on half of his army with most of yours, then go after the other half once the first half is decimated. Imaging the letter "L" where the short leg is where you start your army, and advance across the board, basically broadsiding their army so that your whole ork mob is taking on just an edge of his army and he has to turn and line feed you his units. Works most of the time, and when it doesn't, well lets just say there are seldom any witnesses left in my army and those marines are such story tellers....
If you are worried about casualties, you are playing the wrong army. Orks and all their kit are expendable. That is why we take so many, as we will just grow more. So go out there and krump; kill the enemy, see them flee before you, and hear the lamentation of their players.