Bargaining norms split the world roughly in two. In supermarkets, chain stores, and anywhere with printed price tags, prices are fixed almost everywhere and haggling would just be awkward. In open-air markets, bazaars, and souks across much of Asia, Africa, the Middle East, and Latin America, negotiation is not only accepted but expected, and quoted prices often build in room for it, especially for visitors.
Good technique is mostly good manners. Smile, greet the seller, show genuine interest, and ask the price rather than opening with an offer. Counter somewhere below what you are willing to pay, then move toward the middle in small steps. Keep it light and friendly; treating it as a game rather than a battle gets better results everywhere. Walking away slowly is the classic move and often brings the price down, but only walk if you genuinely might not buy.
Two boundaries worth keeping: never agree on a price and then back out, as that is considered rude in most bargaining cultures, and do not grind a craftsperson down over an amount that is trivial to you but meaningful to them.