This is my first guide so, please help me to do even better :)

I'm Hiroshi Shiba playing EU West server, Silver III (2014) my first year here in Summoner Rift.

My build is conservative, I will have quite MR and Armor both in early then in late thanks to some defense rune so AP and AD champ could be handled
Quints of AP and Marks with magic pen help do some damage with crescente strike (I use to poke and push back champ in early lane phase)

Defense 9 point are a standard and help to sustain lane at early phase.
Offence i prefer to have 4xSorcery to have good CD reduction, a good choice could be also 3xSorcery and Spell Weaving (1% AP Damage ad every basic attack) to have 3% burst when you decide to start your combo and kill

I build two start depends of enemy mid champ: AP or AD.
With AD champ I need to reduce damage so I start to build armor and run for Zhonya to avoid some killing ulti as Zed or Talon
In every way I will build Sheen to grant extra mana and damage as I reach lvl 6 with Chalice of Harmony to have manaregen to sustain my attack action (I know, I spend too much mana to poke and play quite aggressive) :)
Mid game start when I have Lich and Zhonya and start to buld my 3th AP item (Rabadon usually) and complete Athene's Unholy to have CD reduction and also 60 extra AP
Situational items depends how the game goes. If you are the favorite focus and you die a lot, Guardian Angels should be the right item, otherwise Rylai is a good 100 AP with 400 HP and also a good passive.

No words for skill sequence, Crescent Strike is the damage dealer and Pale Cascade help you to do damage and stay alive so I maximize these.
Level 4 is for Moonfall to stop channeling ulti (kata don't kill me!) and prevent flee

Distruptive Combo: Q+R+W+R and Lich Bane. What else?
Diana don't have good spell to leave fight, except of a Lunar Rush to a minion to try to evade.
You must count on your burst to kill and a good mobility if you use Crescent to mark enemy and use Lunar on it (CD reset is a good thing) to low life and get a good chance to kill with full combo.
With Zhonya and Moonfall you could avoid almost all killing ulti like Zed (Zhonya) and Kata (Moonfall stop that)

Farming is quite hard if you have some range champ on enemy side (Xerat or Heimerdinger). I will use Crescent to keep it in range (usually mage champ) and use your Moonsilver Blade to clean lane from low health minion in a row.
Until level 6 is hard to kill but not impossible, Crescent and Pale Cascade will help you to do some damage and protect your life.