One tip is to try to always save your teleport to help your team. Never TP to lane unless you need to early to save your tower or avoid falling behind in XP. Ask your support or adc to ward the lane brush near the enemy tower in bot lane, and when the enemy bot lane pushes you can TP behind to make a play. This usually works really well in low elo. This will hopefully help your bot lane get ahead so they won't die as much. It can also get you dragons.
Roaming mid can help after you pushed the wave as you can be there to countergank if the enemy jungler comes. This can be a good strategy if your mid is getting ganked a lot.
In most cases if your teammate(s) gets picked off and dies in the mid/late game you have to back off and play safe until they respawn, but sometimes the enemy team will just all go push mid/baron/dragon and ignore you in which case you should usually push really hard and you can hopefully trade towers.