This will be broken down by army. Since I'm the only person I know who plays Salamanders this is all from trial and error. And just because these work for me, doesn't mean they'll work for you. Think of it as a broad outline to work from. That said, let me get to the good stuff:
I play Space Marines, have always played Space Marines, for one major reason:
Firepower.
The Space Marines have the greatest firepower/model raito of any army going ('cept maybe Tau, but they arent out yet). I used this to great advantage when I was playing Dark Angels, and I tried to follow the same pattern with the Salamanders (Shoot them till they're dead, then throw more firepower that way to make sure.). While this was wildly effective with the Dark Angels, it's not really possible with the Salamanders.
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On the lack of las-cannons:
The Salamander's inability to take las-cannons in thier squads means less tank
killing infantry, and more up close multi-melta action. The high point is that
it gets interesting trying to position a tac squad so that it's meltas can fire
with effect. The downside is you could just pick up a missile launcher and go
to town. However, the missile launcher may work well for taking out rhinos it's
not nearly as effective as the "dead 'ard" vehicles like the Land
Raider. I say skip the old thought pattern and embrace mobile tac squads.
I don't normally give Rhinos to my tac squads, I just try to keep them in cover
and keep them moving until they get a good firing position. In addition, with
3rd edition the emphasis is on close combat, and often as not, the precious
troop carriers are keen to avoid the 'big, visible' guns, so A tac squad hiding
in the forest is likely to be overlooked/deemed less a threat. Until you pull
out the Multi-Melta mojo and vaporize the transport.
After you do that a couple times, people will begin to actually slow down in thier approach, so as to avoid getting into all the kill zones.
Conclusion: Lack of las-cannons is a strength.
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General Strategies:
Having played Space Marines in three different editions of 40K, I've seen tactical dogma come and go (Shoot the Zoats first!/Stand back and shoot them dead!/Assault! Assault! Assault!). This gives me a broad spectrum of startegy to try.
With the Salamanders the optimal mix for any points set, against any army, seems to be a pile of long range firepower, with a 'dead 'ard assault to clear up the stragglers and open up positions (Ex: In a recent game vs Space Marines I parked my devestator squad on a hill and proceded to pin down and take out his defensive forces while my Chaplain and my veteran squad ran to engage as fast as they could. When they finally got there, there was virtually no organized resistance.). The Salamanders shine at long range (24" and greater), but are wildly devestating close in (24" and less) due to the preponderance of flamers, melta's and plasma guns. And when they finally assault, theres not much that can stand against a tooled up Chaplain.
Before I start any game I designate one squad to be a glorified target (normally a tac squad), their goal in the game is soley to get people to shoot at them. Most people I play respond to being shot at with firepower directed towards whoever shot them. This gives me an opening to start creeping up and getting into position.
A Multi-Melta equipped tac squad can do some pretty incredible damage if properly set up, or can just deter any heavy vehicles from getting near them. This gives you the opportunity to set up some 'funnels' that allow your devestator squad to fire at full effect (you did take devestators, yes?)
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Against Tyranids:
I've been playing against Tyranids quite a bit recently, and I've come up with a couple of things that work well.
1) In addition to having a firebase it seems to work well if you have a squad or two mounted so they can run around and assault things. The squad I normally use for this is dependent on point size (2000 points or less- tac squad, 2 flamers, attached HQ. 2500+ I use a tac squad, 2 flamers and my command squad. If they both hit the same brood, watch carapace chunks fly.) and transport is a matter of personal preference (although I've got a love thing going with Land Raider Crusaders right now.).
2) Shoot the Big Ones is virtually useless because if you actually spend time doing that, the stuff that's fleeting of claw will wander up and drop 32+ attacks on your squad. Shoot the Big ones with your devestators. If your opponent has his synapse creatures spread out across the board, kill them as quickly as possible from one side sweeping across. Gaunts are your friend when they have to take morale tests. Direct the rest of your fire at whatever looks like it's getting into an assault position. Pay extra special attention to things with rending claws (like Genestealers).
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Against Eldar:
Eldar. The very name brings chills to any Space Marine player. Pointy eared gits. Here's how to bring them to your level:
#1. Put a Tatical Squad in a Rhino. Hide the Rhino in cover. Eldar players like to try to move guardians in close, and with 12" assault 2 weapons, I can understand it. When they get to 18" or so, move the Rhino out of cover and Assault them. They die.
#2. At 1000 points or better always take devestators, because you can be sure that any half decent Eldar player will be taking at -least- 1 Wraithlord. I'd reccomend a las-cannon, plasma cannon, missile launcher, and heavy bolter. It's a good spectrum of killing potential. Also, make sure it's 10 models.
#3 Predator Annhilator. It won't last long, but if you get lucky and the dice gods favor you, you will kill a Falcon or two first. You could also use a Land Raider for this, but it's kinda expensive as a vehicle killer.
#4. It helps to remember that Eldar players, as a general rule, count on thier entire army and swift, well timed actions. This is where you can totally throw them off. Theres various methods, but my favorite is, by far, dropping an Assault squad with flamer next to some guardians or lightly armored aspect warriors. Watch the Space Elves burn. Watch the player gack in dismay as his carefully layed plans are messed up and now he's got a serious threat to deal with. You can also use terminators for this, but against Eldar theres better uses for them...like hunting Dark Reapers.
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Against Necrons:
Treat Necrons like Space Marines. Just remember that they throw a lot more firepower around. Try to get power-weapon armed characters into assaults with them. They don't do so well. Necron players hate assaulting as a general rule, so use it to your best advantage. And buy Signums for your Tac Squad sergeants if you have heavy weapons. You'll need them.
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Against Space Marines:
This is pretty straightforward. Just stand back as long as you can and pound them. Not many other chapters can put up the kind of accurate heavy weapons fire that the Salamanders can (take Signums). By the time you roll your Chaplain with a Thunder Hammer into the remnants, they fall like wheat. The only chapter that give me trouble is the Blood Angels, but I've begun countering them by assaulting them. It cuts down thier effectiveness by large amounts. I suspect if you play against the White Scars you should probably be assaulting them as well.