You can probably find out the items you need to get from other more experience Puck players..but I will try and give u advice from my experience with the hero.

Many people play puck as a straight out damage dealer. They like to get ethreal blade and dagon lvl 5, but personally I usually like to play her as a set up sort of hero with a shit load of mobility. Remember. If the enemy team has very few stuns, pick thrives. With a full mana pool, shes about as mobile as Storm Spirit, due to some 6.86 buffs.

So back to the set up hero playstyle. The only thing I find bad about the damage dealer puck if the fact that if your in a losing game, its very hard to acctually build up enough momentum and gold to get the items and levels needed to be a pos 1 or pos 2 carry. That's why, its usually a safe bet to go set up puck. What i mean by this is, get a tonne of mobility/helpful items..

E.g. euls

Blink

Force if they have stuns etc

All that stuff.

This way, you can get a nice dream coil of without suciding. Your not like veno or Venge where you ulti and then you die. You have infinite possibilities of escape and annoyance. This is not to say that DONT go dagon or ethreal blade. But many pick player I see usually go dagon lvl 5 first Item after blink or something. Dagon is a good item, but you should prioritise it. As it hurts the team. Maybe upgrade it every once in a while. But there is no reason to go lvl 5 when lvl 3 is acctually enough for mid-late game. If it goes further, sure, upgrade it.

Ps. Always Max your first skill first. Then I like to get 2 point in her third skill, but then Max 2nd skill next and finally third.