As soon as the enemy team starts overpowering one of your lanes, plan an assassination, as soon as they get close to your ward warn your team mate that you are coming to feast on the enemy flesh (This applies to every lane).

Your role in team fights is pretty clear, you get in, jump right on top of their AD Carry, get out, wait for cooldowns to go off then strike again to help your team.

If your team has enough CC, you will be able to kill and assist on killing (use W often as it slows them down)

Pros

+ Amazing burst damage
+ A well timed leap can lead to
insta kill for your team (2v1)
+ Great Mobility
+ Great Escape Mechanism (E then W and run)
+ Good Kit

Cons

- Pretty Squishy (until frozen mallet or other def. item)
- Only CC is Void Spike and it ain't a Hard CC
- Not of much use in teamfights (unless really feeded)

As soon as you feel confortable with how the game is going, feel free to engage a fight.
Ask a team mate to come around and let it all out (just be aware, do this safely, like if your lane is getting pushed, ask for ganks and the gold will start falling).

You can be pretty good at chasing down, but do this only if you're sure to kill as it can backfire and you end up killed and without kill (do the combo then ignite and if in trouble just leap out or at the utmost end of need flash out)