As a jungler:
-If a lane is ripe for a gank, gank it. Your job is to help your team. If your lane is pushed back, and the enemy isn't warding or you know where their ward is and can get around it, go gank.
As a mid:
-Follow your lane. If your opponent shoves the lane and then leaves, odds are they're roaming. Quickly get your tower out of any immediate danger and follow them. You may or may not end up counter-ganking. Sometimes, simply showing your presence gets everyone to back off and everything returns to neutral. This isn't a waste of time. This is teamwork. Depending on your elo, a lot of people demand MIAs and then don't react to them. It should be obvious when enemy mid is MIA to back up and play safe, but most people don't. Until you reach a point where teammates are capable of thinking, following your lane is usually better. And you should know where your lane is going because you've been warding.
-Ping to alert your team to your presence. Yeah, yeah map awareness, but if your teammates are in a volatile lane, extra units of brain power may be focused on the struggle in lane. Pinging can make the difference between a nice double kill with assists and a team derp.
-If your jungler says "wraiths then bot" for example, start making your way bot. Especially if your bot lane is behind, a 3v2 can be risky, but a 4v2 has a high chance of playing out in your favor. Moreover, have a four man presence can often deter the enemy jungler from coming in for a clean up while three extremely weakened opponents may allow him to pick up a triple kill.
-Value your tower. Don't over value your tower. Outer mid tower has strong strategic importance for vision. Sooner or later, outer mid tower is going to fall in all but the most one-sided games. Losing your tower gives the enemy team a nice chunk of gold. Leaving your other two lanes to fail gives the enemy team a win. If you can see enemies moving in for a gank on another lane, it can sometimes be a better trade to lose the tower but help your team. Ultimately, it's a judgement call. But teams that scratch each others backs win more games than those that don't. Also, know when to anticipate losing your tower first. Melee assassins like Kat or Fizz will have a hard time keeping ranged lane bullies like Cass or Zyra off their tower. If you've seen this heading into the game, prepare to help your team in other ways since you will probably give up your tower sooner than the other mid.