Lunara isn't a champion so easy to use, so i'll try to give you some tricks to improve your game with her.

The first thing you have to understand is that Lunara has't got a lot of mobility, she's so low to change lane or to came back after a recall, so when you are escaping from someone remember to drop him by his horse with your Q.

An other thing you should learn is how to use your E, it could be used in two ways:

1 The first way is the standard one and consists in using it to give to you and to your team vision of a specific area of the map.
2 The second way to use it consists in using it to defend you or an ally form an enemy spell (for example blocking the grab of Stitches or the W of Li-Ming).

The last thing i'll tell you now is: remember that a full poisoned enemy isn't dead until you see him on the death countdown! Because he could be healed or could kill you also if full poisoned...

So let's make a list of pros and cons of Lunara:

Pros

Hight damage
Hight focus whit the Aggressive build
Nice escapes

Cons

So squish
Low mobility
Damage smeared in time

So have fun with her and remember:

THE HUNT IS ON !

This should be the standard one, but it always depends on the team you are in or against (i hope you are able to understand when to go aggressive or safe XD).

With this one you enter in the middle of the teamfight (with your final) so always remember to have two stacks of it to quit as easily as you enter, other way you could die quickly.

Furthermore remember that you're an assassin so just don't focus tank so much but focus on other assassins or on supports.

Lunara needs a lot of training to be well used, i'll say you the normal combo, but it's very versatile :

Q-R-W-AA-R

(AA meanies auto attacks)

This one should be taken if you are losing the game, in fact this just make you dealing a lot of damage without risking so much.

This final has a real bad con: you can't focus so accurately and you can't reach the enemy behind (so all the those an assassin should kill) i mean supports and some assassins (just think about LT.Morales or Li-Ming)

The normal combo is :

Q-W-R-AA-R-R