I don't want the answer to just be defends, captures, or damage. Discuss.
What makes a good Lockdown player?
Being good in LD is not all about spamming, cloning, or hammering. It involves something called 'skill'.
To acquire this 'skill', you have to practice with every class and see what one you don't die with as much as the other classes. Then, equip your glove trinkets, then, read movement on the map. See people already taking a point? Don't go to that point. See one of your points being taken? Take it back. While you are busy not dying, see how you can use how people move to your advantage. Start killing them like Feller. You will definitely need ASI if you are not striker (speaking from a swordies PoV).
I have written a guide on one of the classes. http://forums.spiralknights.com/en/node/82028
And then I rage at people killing me with AA and Glaciuses. http://forums.spiralknights.com/en/node/83947
Skills?