So my friend wants to play puck. What are some things that I should tell him about him because I have no clue.
Puck is one of my favorite heroes.
Phase Shift at level 1, unless you have some extremely weird situation, there's no way it won't be useful at level 1. If something bad happens and you need to dodge something big, BOOP! Pop that Phase Shift at the right time and you're good. Just leave it at 1 until later. Max Orb, grabbing a point in Waning Rift at 4. You could also argue for maxing Silence too, but it's really up to you. Grab Dream Coil whenever possible.
You go mid, you get those fast levels, and you gank. Ganking with Puck is ridiculous and most of the time gets you a kill. Generally don't start ganking until 6. If you've been harassing your mid opponent enough though, and think you have a chance, you could use your first Dream Coil to kill them. Very hard thing to get away from if they're pretty squishy.
As for items, Bottle if you're mid, and Power Treads or Phase Boots as your boots. Arcane Boots if you're not mid. Get one Bracer, and a Blink Dagger is your most important item. You can turn the Bracer into Drums later, which is pretty useful. After that, you have some options. Bloodstone is good in general, but I don't usually go that route. I usually go Linken's or Scythe, depending on the other team.
Now here's the cool thing about Puck: You can walk out of DAMN NEAR ANYTHING alive! All you have to do is time your Phase Shift right. Once you have Phase Shift maxed, the duration is longer than three seconds, which is the cooldown for Blink Dagger if you get damaged by a hero. You can pop the Phase Shift and Blink away as soon as it's ready! Mass AoE teamfight? Cast your spells, Phase Shift and get out of there. Sven wants to throw his Stormbolt at you? BOOP! You can completely dodge that shit and it hits nobody. You can dodge anything with Phase Shift, because Phase Shift basically makes it where you don't exist. Any debuffs you have on you don't apply during it. Sniper ults? Pfft. Last Word? Just watch the debuff, and when it's just about up, Phase Shift and you completely negate it.