"Skilled" assumes that mistakes are minimal on both sides - no one is being pulled into an obvious gank, everyone has an escape route, and teams coordinate effectively to protect and support each other while advancing their strategies.
In all cases flexibility is the most important aspect of play. Pursuing your strategy at the expense of actual events will get you crushed if your opponents know what they are doing.
That said, I see people throwing themselves madly into battle to protect the Brilliance Flag - you shouldn't sacrifice your DG for something of little importance. If all of the below seems like common sense, congratulations, you know your Cataract strategy and I'm not talking to you If any of it seems wrong let me know, always happy to learn something new...
Offensive Priorities (map):
1. Fortitude Flag (lockdown*)
2. Center Flag (for WarRank and Experience buff)
3. Outer Tower on Opponent Goldside
4. Opponent Gold flag (lockdown)
5. Outer Tower on Opponent Celerityside
6. Opponent Goldside Towers
7. Opponent Goldside Portal Flag (lockdown in conjunction with unit upgrades or to weaken opponent unit upgrades)
8. Opponent Celerityside Towers
9. Opponent Celerityside Portal Flag (lockdown per above)
10. Enemy Citadel
*lockdown - you don't ever want to lose this flag for more than 45 seconds. If being pushed off the flag then you should lock it. If you lose it you want it back ASAP
Defensive Priorities (map):
1. Fortitude Flag
2. Goldside Outer Tower
3. Gold Flag
4. Celerityside Outer Tower
5. Back Celerity Flag
6. Goldside Towers
7. Goldside Portal Flag
8. Celerity Side Portal Flag
9. Allied Citadel
Citadel Upgrade Priorities:
1. Mint 1
2. Tower Regen 1
4. Exp 1 (optional - control center if you go this route)
5. Angels thru Catas/Giants
6. Unit Armor and Damage
*Please DON'T buy Death timer upgrades or currency upgrades past level 1. Building upgrades past level 1 are extremely situational - unless you know why you are buying them don't*
Demigods - All DGs are viable on Cataract in 3v3, though some burn out early. Common anchors as of 8/13/09 are Sedna/UB and Oak/Erebus. In most cases you want at least one General and one Assassin, after that it's playstyles, team dynamic, and opponent counters.
No verdict yet on whether Carry DGs should get the solo lane for greater xp. I expect it's extremely situational.
Fortitude Flag is the prime Dark offensive lane and Light defensive lane, because it leads to the Light gold flag and has a gamechanging 15% hp buff. Dark will always have two DGs in this lane, with the faster or less solid one swinging mid as necessary. Dark wants to control Fortitude, knock over the solo tower, cap and lockdown the Light gold flag, knock over the gold towers, and *eventually* take the portal flag on this side.
(It's important if Dark has momentum not to cap the portal too early - it forces Light to counter, which means they will roll up the lane with all three DGs if necessary. Much better to keep the gold flag and stay inlane for the xp)
Light might need two DGs in the Forti lane to counter Dark, but if at all possible should push the Brilliance Lane hard and early to gain access to the Dark Gold Flag. Once the Dark gold flag is locked down or at least accessible, one DG should relieve the Fortitude defender and together they should concentrate on defending and pushing the Forti lane for the Dark Celerity Flag. As much as anything this is defense-by-offense - Light can't afford to let Dark control this lane. Whenever it can Light will focus on razing all Dark structures in or close to the lane to prevent Dark port access.
*Please note - It is possible for Light to mirror Dark and pressure the Brilliance portal instead if they are willing to operate at a 15% health deficit. Midgame that can be a 700-900 hp difference, but it isn't insurmountable.
Midgame Center - if the lane fights have been settled and everyone has a port scroll for defensive maneuvers your team can pull all spawning enemy reinforcements to the center flag for xp and to allow your units a shot at the towers mid. Taking down these towers allows your reinforcement streams to converge, greatly magnifying their effect. At this point you should be looking for Catas with damage upgrades or Giants.
Lategame - create pressure at the enemy's front door either through grunt upgrades or DG influence or both to the point where the enemy must commit to the center. If they are any good they will port to threatened portal flags, so coordinate movements so that their defense is either too late (run two DGs to the flag, cap and lock before they can port in), misplaced (feint for one portal while your ally locks the other), or costs too much (defending the portal means the center is weaker and gets pushed hard).
Once you have locked down an enemy portal and all allied portals and have catas it is very difficult for your opponents to win. GG everybody! Please don't let me catch you squabbling over the Brilliance Flag anymore
Some of my strategy posts:
Tips 5/11/09 (some outdated)
Kiting, Exposure, and Dancing
Thanks for reading