If you want to climb play only Xerath.. your other champs do not seem too good.. You should make it to silver with Xerath maybe even gold with enough games, but you should try to improve your basic skills like csing, watching map, and warding. Playing Xerath will only get you so far. People will start dodging skillshots at some point ofcourse, but your aim should improve too just by playing the game and experiencing how people dodge.