How to improve fps skills

I'm awful at fps games. I really suck when playing CoD MW with my friends. How can i improve my skills? Any specific game to practice aiming, moving, dodging, etc? I mean, some game that you have challenges to beat, like 'shoot x targets in x seconds'

Use a search engine for "Aim bot". Then lose all of your friends: you cheating, AFK bastard!

i don't want a bot, i want to improve my skills. i know i can, i just need the right training. aren't there any games with shooting challenges?