Map Tactics

Hostage scenario.
Terrorists should gather the hostages, or at least stay in a position to keep the CTs from them. The CTs must rescue at least 1 hostage, the others can be killed and the CTs win the scenario. So, either kill all of the hostages or make sure the CTs get none (it's better if they're the ones who kill them). Terrorists must be patient and should not rush. Rushing in a hostage map should only be used as a surprise tactic or, to circle around the back of the CTs.

CTs, on the other hand, should stay together and concentrate their firepower at the most vulnerable points in the T base. But, there is an optimum number of CTs per choke point and on a map like cs_italy, CTs should be able to cover more than 1 choke point. On some maps, like cs_siege, there isn't much choice, but on a map like cs_italy, CTs can easily overwhelm an undermanned T base, especially if most of the terrorists have decided to rush.
If the CTs have the hostages, then terrorists should camp at the hostage rescue points and ambush the CTs as a last resort.

Bombing Scenario.
CTs should camp the bomb sites and be patient. The terrorists must bring the bomb forward, plus, the CTs still get a second chance if the bomb is planted as they can still defuse the C4.
The terrorists should decide at the first moment whether to camp or rush, as the more terrorists there are, the greater chance they have in winning the round. If they rush, they must rush as fast as possible to the (predetermined) bomb-site, overwhelm any opposition with sheer numbers (and grenades) and plant the bomb (preferably on a box). If the terrorists decide to camp it, then they must pick off the CTs while keeping the bomb in their possession.

The round usually ends with either team eliminated, rather than the bomb being planted, but if things have gone well, then the remaining terrorists should outnumber the remaining CTs and be able to plant the bomb.
If the bomb is dropped, the CTs should camp it. Likewise, the terrorists should camp the bomb once it has been planted.

Assassination scenario.
This is essentially the bombing scenario with the roles reversed. However, the VIP should hide and stay at full health, rather than running with the CTs. While the VIP is hidden, the map becomes a simple team death match.