Trick is to get near the flag in the rush but do t go for it. Lie close and wait. When someone else scores or its returned grab it and go.
Man, capturing the flag is so tough. Everyone goes for it so it's hard enough just to be the one guy on your team who gets to carry it, let alone cap the damn thing. I wonder if eventually people will stop being greedy with it because of the assignment. I've even been killed while carrying it by a teammember in hardcore because they wanted to be the one to cap it.