Welcome! The best bits of advice I was given when I started were:
Buy the book before the coin. Read, read, read if you are serious about collecting.
Buy the best grade you can afford of a particular coin.
Finally if you buy coins graded by third parties (slabbed coins from LCGS, PCGS, NGC, ANACS to name the mains ones) buy the coin not the slab. That is to say dont let the grade on the plastic deterkine if you feel its a nice coin.
Good luck and I hope you enjoy this great hobby!