The game has scoring built in to ensure that the competitive spirit never dies. Points are scored each go for the amount of damage that is inflicted upon another Titan. The points vary depending on the relative tech generations of the Titans involved.
A Clan will receive 1 point for damaging a single unit on an enemy Titan if they tech similar to the targets tech. The amount scored is dependant on the offensive values of the Titans involved. The section below shows how the techs effect the pts scored when fighting another titan.
offensive = Math.round((0.8*weap+0.6*shield+0.5*comp+0.4*(engine+material))-16);
The points scored are simply the the defendors offensive/attackers offensive. If this is less than 0.5 then its rounded down to zero.
Note that titan offensive values are used in the calculation of clan might.
Play with it and you will see that generally attacking older titans can pull in the rewards, whereas attacking younger titans may not gain you any points.
Every fourteen turns is a tourney, the scores for the tourney are worked out and converted into an archive score where they are averaged with previous scores. The score for the tourney will determine the maximum size that your clan is allowed to be for the following tourney.
As was pointed out by Rob, a long slide could seriously effect your score and thus your clan size. So any tourney in which your clan was absent for 5 turns or more has a safeguard implemented to ensure that your clan size will not decrease. To put it another way, slide out for 5 or more turns in a tourney and no matter what your score your clan size cannot decrease, but if you still manage to score loads of points it can increase as normal.
The amount that your clan will grow or shrink is determined by:
((tourney score - current clan max size)/(current clan max size)) *10
For example, a clan with 30 Titans score 45 points in the tourney. This will allow them to grow by
((45 - 30)/(30))*10 = 5
For the next tourney they will be allowed to grow to be up to 35 Titans. If no points are scored the maximum clan size will shrink back towards 30 again.
For example, a clan with a maximum size of 45 scores 15 in one tourney, they will shrink by
((15-45)/(45))*10 = -7, so shrink by 7
A clan may only ever grow to a size of 100 at most. This ensures that the comms between player and server do not become too great for each turn and 100 Titans is more than enough to keep things interesting.
At the end of every tourney your score is amalgamate with the existing historic score and then reset to zero. The historic score is determined by:
historic score * 0.9 + tourney score
Which means it will take 10 tourneys for new players to be on a comparative scoring level with existing players! Ladders will be produced on the Faraway web site.
Only through attacking and damaging clan halls do players score ranking points. The score for hitting a clan hall is worked out as normal but is instead added to the ranking score. Ranking scores are far more rewarding and important than normal scores. For each two ranking points scored against you you will lose a single ranking point of your own. You will also lose ranking if you fire upon yourself or self destruct your clan hall.