As skarner, In the late game, continue to look for flanks with your E and R. 

Play around your Ultimate cooldown in the late game. Avoid team fighting when your Ultimate is down to ensure that you’re useful in team fights!

Group with your allies as the enemy will just force an engage and kill your team while you’re not with them.
 As skarner, At the end of the game, keep looking for flanks with your E and R. Play around your Ultimate cooldown in the end of the game. Avoid team fighting when your Ultimate is down to make sure you're useful in team fighting! Group with your allies as the enemy will just force a commitment and kill your team while you're not with them.