As lissandra, After your bot lane has moved to the mid lane, rotate to the bot side of the map or somewhere else on the map so you can continue to farm and gain XP. 

When no team fights are occurring, go to a side lane and push. It’s important that you continue to farm during the mid-game so you can get your items as quickly as possible. Do not just stay mid if you can’t get anything done.

As you’re good at getting picks and killing isolated targets, try to ambush and assassinate enemies who are alone or walking around Summoners Rift alone. After killing someone, make the call for a nearby objective. As lissandra, After your bot path has moved to the middle track, turn to the bot side of the map or somewhere else on the map so you can continue to grow and win XP. When no team fight occurs, go to a side track and push. It is important that you continue to grow during the middle game so that you can get your items as quickly as possible. Do not stay right in the middle if you can't get anything done. As you are good for getting peaks and killing isolated targets, try to lure and assassinate enemies who are alone or walk around Summoners Rift alone. After killing someone, call for a nearby goal.