The method I've always tried to get guilds to use was like a military systems.
We have front end attackers, back end attackers this requires good timing,members,and co-operation. As well as 10-20 online users.
Take your guild/2, (divide your members into 2 sub sections) then tell each member if they're in group A or group B. (Leader will be group A). You want to mix it up have good members in both groups(A,B).
When attacking get group A and group B in the same area and on 3 group A takes they attack. This is where it gets tricky, when group A has 1-3 members left someone must say in GC "Group B attack" then group B will attack, keep doing this until taken. This method is effective because if the whole guild attacks all areas to hit flag are taken which leaves attackers standing there clueless.
It's hard to use this at the start, but once you master it its helpful!