This is what i could do at level 14 summoner, thats why only 14 skill points used
Its Simple Build and has all the elements an assassin needs

-Attack Speed
-DPS
-Crit chance
-Damage
-Life steal

Strategy is simple, Quick in and Quick out.

Do's
-Buy dagger,Take Mid lane and level up fast
-Level up Blinding Dart (BD) and Toxic Shot(TS)
-Harass the opponent player in your lane, with BD to keep him from getting XP
-Concentrate on Last hit on creeps, You should have atleast 1000-1400 gold before you hit base for the 1st time with about lvl 7-8
-Finish berserker's greaves and you should have enough gold to buy 1-2 daggers
-You can now easily kill Non-Buff creeps.
-Go for kills in mid lane and Finish Malady
-Once You finish Malady you kill Buff Creeps with Noxious Trap (NT) and BD
-To get more kills at MID, put NTs on Sides so that creeps Dont run over them
-Time to move to Top and Bot Lanes, also Keep killing neutral creeps whenever possible
-By Now zeal Should be finished, Buy Vampiric Scepter , Madred's Razors and 1 BF swords in the order
-Vampiric scepter; so that you can add some life steal
-Madred' Razors so that you can farm for BF sword
-BF sword for Damage
-Finish Phantom Dancer then The Blood Thirtster
-Go for another BF Sword, Finish Infinity Sword
-Final Item is Madred's Blood Razor or You can go for BLack Cleaver, Lich Bane, Hextech Gunblade as final item
-Always USE BD to start attack, as opponent will miss 1st few attacks
-You dont need to slow Enemy heros, Just press W (Move quick (MQ) and Keep using BD
-If you get into 1 vs 1 standing fight, use BD and NT
-Check Mana/Energy of Enemy, If its out...You can pawn them
-Also you can choose Wit's End as one of the items early game, if there are too many mage class champions, drain their mana and they are useless.

Don'ts
-Never Follow a Enemy Hero Beyond tower, 3 shots by tower and you are dead
-Never get in the middle of ganks, stay away enemy skill range and single out heroes and kill them
-Never Run ahead of your team while going for a Gank, as most of them tend to with MQ
-Never USE NT when Multiple heroes are chasing you as it slows you, Instead Use MQ and escape
-Never try go Invisible when trying to escape, as its almost impossible to get 2 secs out
-Never Wander at low health, as you will be 1 shot skill
-BE Smart and don't try to save heroes if it risks your death
-Stay away from Disablers, and Wait till they use disable skill on someone else

Its an Easy and Basic Build, and if you play well, you'll get 15-20 kills easily