Long range champions going against close range champions

Hello I am a new player and I've been playing Xerath and other long range champs a lot lately. Sometimes when my enemy is a champion with dashing abilities or high movement speed such as Garen, Zed or Riven I die a lot since there's literally no movement speed for these long range champs so they just jump on me or stun me and the next second I'm already dead. Is there any strategy or tricks that could make me safer at pushing and fighting against them? Please help me out