I start off with the mana regain rod and the the 2 hp pots to survive till I get to level 6. I don't go back to base till I have my ultimate. By that time you should have enough for the attack speed boots and close to gear the mana tear. Provided you don't suck you should be able to get at least one kill, which will give you enough money after the tear of goddess and attk speed boots to rather buy a +45 damage sword or at least 1 +15 damage sword. Sometimes if I havn't made enough gold I will buy two +15 swords and then sell one later on for the +45 sword keeping the other to make my phage. I get the phage after the +45 sword for some hp and slow chance on attk. By this point of the game unless you're getting lots of kills you might need some armor so I get the chain vest next, which will be used to create an atma's later. After that I get the pick axe for more damage and then save up till I can finish the frozen mallet. Now you should have the pick axe and the +45 sword at this point so it won't cost much more to finish and get the infinity edge. After the IE I finish getting the atma's. Giving me enough armor and hp to survive with a very strong attack. The atma's usually adds around 54 AD after the frozen mallet. End game I have about 2.6k hp and after buying my last IE I have about 340 AD, critting at around 1k. Which the recent updates I don't buy cooldown reduction items as they're pretty short.

Common sense, whenever action isn't going on I jungle a lot for money. I will get both Red and Blue buffs, but only if no one is hunting the Blue buff. I will always get Red. It's best to farm a lot if you're not getting kills.

As an assassin, unless I have my final build I don't lead the pack. Your best help is to stun enemy's as much as possible, and using heartseeker strike after is a must. I harass with spear throw and on team fights stay back and use my ultimate and then jump stun and HS enemy's.