Class mix – Like pretty much every map in Team Fortress 2, the most common reason for defeat (or stalemate) is an inefficient class mix. When you see your team has 3 snipers, 5 engineers, 0 medics, or 1 soldier, you need to realise you have a problem and not only/necessarily change your class, but ensure your team rectifies the issue. You should have a maximum of 2 snipers and 3 engineers, and at the absolute minimum 1 medic, very preferably 2. Soldiers, demomen and heavies make up your front line, so if you do have 2 medics, make sure there’s enough attackers for them to heal.
Defence – The most infuriating situation on 2Fort is when the enemy picks up your intelligence but no one seems to notice – the tops of the ramps are left clear, snipers keep watching the enemy balcony and your team keeps fighting over the bridge while your briefcase is waltzed back to the enemy base. When you hear “the enemy has taken our intelligence” there is a single, obvious course of action – defend! And get your teammates to defend with you. The best places to defend are halfway up or at the top of the two ramps from the basement – see the next tip for an efficient method of cutting off the enemy case-carrier.
HUD arrows – Something that is often overlooked (not so much a mistake as an unawareness) is the arrows on your HUD that spin around the team’s scores (see the picture below). These always point to the current location of their respective team’s intelligence (except they’re disabled when you are carrying the enemy intelligence), and they can be used to find a teammate case-carrier to escort, track down a dropped briefcase to attack/defend, or figure out where an enemy case carrier is to cut him off. It is most useful when the enemy is making his way out of your basement with your briefcase, since you can line it up like a compass and work out whether they are coming up the long or short ramp before you even see them. Make sure you alert your team which way they are coming out, since many people seem not to know about these incredibly useful triangles.
Dropping the intel – If you or a teammate has the enemy intelligence and you are under attack or being pursued, it is often wise to drop the briefcase (default L) for a faster teammate, especially a scout, and especially if you are a slow soldier or heavy, or a weak spy.
On a similar note, on the rare occasion that you have the luxury of a medic, and on the off chance that he has an übercharge ready, know that the case-carrier cannot be made invulnerable. Attempting to do so will result in an invulnerable medic that can only heal the carrier. Often a more effective and unexpected manoeuvre is to drop the intelligence (once again L), activate the übercharge, clear out the defenders, then reacquire the case and proceed.
Spy sacrifice – If the enemy intelligence has been dropped outside their basement (i.e. at the top of either ramp or further) and your team is making a push to recover it before it returns, it can be worth having a disguised spy run in behind the enemies and pick the briefcase up. He will instantly be revealed as a spy and promptly executed, but the recovery timer will be reset, giving your team more time to retrieve it. Of course any ground covered by the spy is an added bonus. Note: a scout can occasionally be used for the same kamikaze purpose.