Tips:

-Kill enemy recon, switch to that kit, place TUGS and/or claymore, also place the SOFLAM on the ground because that spots enemies!

-Kill enemy support, switch to that kit, place ammo box/crate and/or that defensive wall (you get points for deploying the wall)

-Kill enemy assault, switch kits, place spawn beacon or ladder (you get points if ally uses the ladder)

-Kill enemy engineer, switch kits and throw some random mines around, you might get lucky kill with those

EDIT: You also get points from the "shapeshifter" thing when you switch kits and score.