Kotov: How to think like a Grandmaster - is a must to every serious chess player, Suliman - endgame study, and Masetring chess openings Volume one to four. Also you need a good chess software to really improve - Hudini or Commodo
Earliest published chess book that you think is worth owning
Sort:
You can either have read it, own it yourself or even go by reputation if you want. I'll start, I've had a look at Laskers Common Sense in Chess and think it is excellent