Companies will regard people with good negotiating skills as a valuable asset to their firm. Negotiation is not about playing hardball for the sake of appearing to be a tough negotiator. Be willing to adjust your expectations based on your market value. At the same time, do not accept an offer that does not make you happy. This serves neither you nor the company.
Nobody wants to be or employ an unhappy worker.
Get the employer to offer the first concrete number. You short-change yourself and look uninformed about your market value. The number is too high. You appear greedy. You lose the position to a more reasonable candidate.