Ive mained mid for a long time but this has been a question that has stumped me the whole time and i cant seem to find anything over it. What do you do when you have a good lead as an Assassin or Mage and the rest of your team isnt caught up with you? I amd silver 3 if that helps.
Buy something that is heavy in damage (
or 
) and wreck your lane opponent. Then roam down to bot and get a double kill, and then take dragon. Your team will mostly likely do whatever you tell them after that.
you go botlane for a double kill you deep ward their jungle so you can go get a kill you go top lane and get a kill you counter gank bot for a triple kill
gg ez
You could roam around and help the other lanes if you have the advantage, and even if you don't you could keep an eye out on the other lanes to see if you can snowball off them. Depends on the champ and playstyle. That's just me.
Like the other comments are saying, share your power with your team. Teamwork doesn't start or end at teamfights, and the jungler isn't the only one allowed to roam (looking at you supports who never leave bot lane).
I generally roam, especially when playing assassins. Assassins just seem more mobile. Not to say you can't do it with mages too, but that's just how I've felt.
But yeah, especially if you've taken the first tower in your lane, roam around and help the jungler gank. If he's taking top, go gank bot or whatever. If you're REALLY far ahead, you could team up with the jungler or support and take an early dragon.
I've seen many challengers who got an early lead in mid grab + 
. I even saw Annie Bot do this and I though "WTF? No 
?"
But his roams were so damn good and he ganked like a beast.
