Need help with hands?

I love tkd and am progressing rather fast, but my instructor and me notice that when i spare my jabs and punching aren't as they should be, im slow when it comes to punching, I can kick like lightning and have long legs but i know they wont last. i do jujitsu as well and feel that if i were to get into a fight with some one it would be wise to know how to us your fist.