I know it is early to be making a Diana build guide but I have been playing her a lot lately and have followed this build every time. i have not gone negative in any of my games with her when following this build. I cannot garuntee that there will be a win but you will be able to do some serious damage and enjoy some early kills as well.

Once you have your ult ("R") you will want to land your combo, which consists of "Q" followed by "R" then into your shield "W". Rinse and Repeat. If your enemy is fleeing try and land your "E" to bring them back to you. If they are out of range of your "E" then use your combo. When playing Diana Know when to use your ult to get the kill, whether or not to "Q" then ult (R) so that it refreshes your "R" right away or to use your "R" and wait for it to cooldown.

Blue will give you the ability to spam your abilities as often as you want and give you that little extra cooldown to throw out your "Q" and "R".

Why Nashor's Tooth?
because it gives you the cool down reduction to throw out your "Q" often and efficiently. it also gives you some early ability power to dominate your lane and attack speed for your Passive to occur when needed.

Lich Bane
is a good choice for after your ultimate, you dash to your enemy and the next attack does some good damage while you wait for cool downs.

You will want to max out your "Q" so that you can poke in lane, which once you have your ult at lvl 6, will be a great starting damage to melt down your enemies.
Grab your ult whenever you can and know when to use it.

Diana is a great champ and will be a huge threat in any game. remember to get Blue Buff whenever possible and to poke in lane with your "Q". Don't forget that combo. She is a champ that really dependant on her ult so know when to use it.