The Flying Beaver:
Post your tips for fighting armies Orc and Goblin here.
Uzkul Werit:
My key bit of advice here would be avoid their magic like there’s no tomorrow. It really is that painful. My last game against them for example. My Great Taurus was inches away from taking out a Rock Lobber. A Foot of Gork slammmed down on him, killed the monster and left my Lord out to get butchered.
And the other thing is this - Black Orcs aren’t that good. They’re on par with our basic Warriors. Infact, Savage Orc Big 'Unz are much worse. 4 attacks basic with two choppas? No thanks! Pretty much any Orc unit will crumble with a little Blunderbuss fire as they will rarely take anything above Light Armour.
Hashut’s Blessing:
Use Bolt Throwers. If your opponent is anything like the one I play against, he’ll take large numbers. A single bolt can remove 6 models at a time. It’s excellent for those panic tests. Also, target shooting at Orcs/Black Orcs. You can fight off any night goblins/goblins in combat if need be, but you’ll be more likely to cause them panic. Shooting the goblinoids has no effect on the Orcs, which are the bigger threat to you.
The Flying Beaver:
Some random tips:
-Small hobgoblin units are great for forcing out fanatics.
-Bull centaurs are a good choice against O&G as they have poor shooting and BC’s will mow right down the flanks.
-Take at least two BB units, they work wonders against O&G.
-Be sure to laugh at their goblins for only having WS2.
Uzkul Werit:
Fanatics shouldn’t be too hard to remove. Once they’ve popped out, swivel some Blunderbussmen in their way. You will always hit and wound on a 4+ (at least for wounding)! And you should be able to get the parent unit hit in the bargain!
AGPO:
As uzkul says, blunders are greeat for dealing with fanatics without wasting your shots, as you can theoretically take out all three and hit the parent unit with one round. But remeber that you only stand a 50% chance of hitting the damn thing in the first place, and those boyz hurt
torn:
against large blocks of goblin infantry try and keep a small hobgoblin unit (even if its just ten man) to flank charge into the side of your combat. most goblin and night goblin infantry i have come accross is usually 40 man with all rank and banner bonus’s. getting rid of those give you a massive advantage in winning a combat.
wallacer:
Be sure to field blunderbuss units in sufficient size to have Stregth 5 shots.
Strength 5 is great against Orcs, and the extra -2 to save is a deal breaker against most Orc units.
bait out the fanatics with hobgoblins. This will disrupt his timing for a declaration of a waaagh.
Use your lord on Taurus to hunt down wolf riders, bolt throwers or wizards.
Use the Earth Shaker to slow down the Black Orcs or Boar Boyz.
Stack a flank if you can. Most orc units can go toe to toe with most things in a CD army. Every time I have won against the Orcs it is because I have broken the line at a key point, usually by a frontal assault combined with a flank charge from a Lord on Taurus or Hobgobs as well as some softening up with magic beforehand.
Be aware that he will be trying to break your line at a key point too, most likely with his Black Orcs or Boar Boyz being led by hard Lords or heroes (if they are big enough). Use the Earthshaker to slow them down and bolt throwers to whittle down their ranks. Divert with Hobgoblins if they get too close…
remember that when planning your magic when building your army that he may well have the staff of sneaky stealing which will take one of your power dice. Factor that in when calculating how much power you will need to get spells off.
The shadow lore works well against Orcs, particularly the spell that gives you a free move and the one that does D6 strength 1 hits (I always seem to do well against Boar Boyz units with that spell).
Lepreh Khan:
Plopping a Terror causing unit behind his battlelines is a great way to force panic across the table. You’ll find that the Taurus’ fire breath is quite good against them as well (and sometimes is a better option than charging into CC)
Most importantly, however, make sure to make the remaining O & G force your slaves after you’ve beaten them into the ground. 
-LK
Dissembler:
My only fear in an O&G army is giants… my friend uses them religously. Always have some bolt throwers to take him down, and a unit of gobbos to slow him when he gets too close. And as was said before, gobbos to draw fanatics and shoot da boyz with blunderbusses/bolts
Bassman:
Being the contrary to a good general I do not usually provide suggestion for tactics but Orc n’goblin is one of my favourite games. Funny, lots of slaves and my best scores ever in Warhammer: I always win
I recently discovered that blunderbusses just need strenght 4 against t3-4 low-no armor troops, so I deploy 10-12 large front and just 5 blunders in back rank. You’ll find how much is funny to cover 40-50 models with just one unit! Killing 5-10 orcs/20 goblins per turn is funny 
Does your opponent field giants or large monsters? My four bolt throwers are waiting for you.
Heartshaker usually hammers the centre of the army, slowing down the main blocks.
Make sure to use hobgoblins to reveal fanatics and hobgoblin bowmen to get rid of them.
My blunderbusses NEVER kill the closest two fanatics and kill only the fanatic next to goblin unit! 
Orc n’ goblin magic could be dangerous even if a little tricky. Bring some defences or your sorcerors and characters will never leave units!
A couple of dispell scrolls and 4-5 dispell dices are ok.
Pump wagons are impossible to deal with blunderbusses as they get only one shot, use magic instead, a couple of fireballs and they are gone!
Be sure to use slaves to disrupt his battle line, never allow him to multiple charge your warriors or expensive units, when Orc n’ goblins fight in masses they could be really dangerous.
Savage orcs could deal a lot of punishment, their weakness is fury… hobgoblins to divert them anyone? 
Once my opponent had a massive unit of 20 savage orcs, I used 10 hogboblins to divert them into a forest and they struggled 3 turns to get out. At the end of the battle they killed only a bolt thrower…
astragoth:
an important thing to remember is that o&g only is good at close combat, they have nearly no archers. so blunderbuses would be great. big uns are not worth 9 pt each. goblins have only 2ws but there are hundreds of them! so the best way taking them is whit weak spells whit many hits, ( or strong spells whit many hits ) like pit of shades.
Burske:
I have played O&G for the past year and have played a couple of tournaments. Here is my insight:
1-Animosity blows. The army will inevitably handicap itself.
2-Kill Manglers. If they reach you, you will be in trouble.
3-Warmachines hurt. If they are a good player, they will have taken savage big uns that have ward saves. This is probably the unit with the points in it (ie;characters). Even with the shrunken head, you will still whittle them down with shooting.
4-We don’t have anything cheap to pull fanatics on their side of the board, but that is the preferred method if you can.
5-The big waaagh spells are pretty tame; do NOT let them cast Hand of Gork. They could drop their savages right on your war machines and that is that. Foot of Gork is cool, but it scatters and is not nearly as scary as it could be.
6-Little waaagh; they get one off, the potentially grab one of your dice, so beware. Curse of da bad moon is an issue, but the rest are workable.
7-Shoot, shoot, shoot. If there is an achilles heel for the O&G it is shooting. They really can’t do much about it.
Anyway, just a few of my cents!:hat off