Lissandra is a teamfight-oriented AP champion , who also excels at killing squishy targets , bursting them down.
Her laning phase is quite safe if you choose just to sit and farm , but also aggressive and strong when you decide to poke the enemy using your Q through your minions and then comboing to death the enemy.
Thanks to the low cd on the Q she also has a great wave clear and fast push threat.

Her kit makes Lissandra a great component for a pick composition team-oriented ( cc train ).
She can initiate with E/flash into enemy backline and W + R enemy adc ( or herself depending on the circumstances ) + Zhonya .
She grants a good dragon/baron pressure and a nice diving potential to the team.

Farming in lane with lissandra is not difficult : her autoattack are quite good and responsive.
Her passive is extremely good and helps her a lot making the champ not that mana thirtsy.
Early in the laning phase you don't want to push , so try to not spam q randomly : use it to not let enemy push the wave / poke him .
When you finished an early morello / needlessly large rod a couple of Q's are enough to clear the entire wave .

Pros

+ Extremely Manaefficient + Good CC train kit + Good Escape Ability with Glacial Path + Great burst damage

Cons

- Hard to Master - Must be played risky to be good - Pretty low Range.

In a teamfight Lissandra can't poke the enemy team . So if you have an initiator follow him as soon as possible , trying to make advantage of the chaos to reach the enemy adc with Glacial Path and burst him down .
Lissandra has perfect AOE cc , so followed by a bruiser as Irelia , Jax , or others can be devastating .
A good synergy is also with Rumble top lane and others champs with desrupting and AOE ulti.