In any negotiation being prepared helps you. How ready you are is proportional to how important the negotiation is to you. Forbes gives some nice tips about negotiating a salary increase in your job but this advice expands to negotiating prices for your products and services.
The idea is that you need to know what the range of your competitors prices are, what differentiates what you do with what others provide, how important those differences are to different groups of customers. Other helpful things are breakdowns of the pricing via materials, time and other expertise.
Now when you have your detail in making a quote don’t use a round number. For the same reasons in the article they are not as believable to a person hearing them. Different people will dig down to different levels and starting at a legitimate non-rounded number going a few levels deeper will get you through 90% of your customers. That last 10% you know how that goes so either dig in or relent and just give them something off but in this case it’s less of a hit.