What preparation usually misses
Most guides give you arguments. Market comparisons, proof of performance, phrasings. All of that is usable and rarely the bottleneck.
The bottleneck is the number. Whoever has no concrete number in mind is not negotiating, they are asking. And a question can be answered with a no.
Part 1: name a number, not a range
A range looks accommodating. In practice it means you have already settled on the lower value before the conversation starts.
Decide beforehand. One number you can say out loud without your voice going up at the end.
Part 2: bring one piece of evidence, not five
Five pieces look like a defence. One looks like a statement. Take the one that is hardest to argue away, ideally with a figure attached.
If you notice yourself collecting and collecting, that is often a sign you want to be safe. Understandable, but it makes the request smaller, not bigger.
Part 3: decide beforehand what you do if the answer is no
Not as a threat, but for yourself. Do you want a date in six months? Do you want to know which condition would have to be met? Do you want to look around?
Knowing that beforehand takes pressure out of the conversation. And whoever is under less pressure talks less.
Part 4: the moment after the number
Say the number and then nothing. That is the hardest part. Most people fill the silence with qualifiers: if that is too much, I know the budget is tight.
The silence is not yours. Let it stand.
If you prepare it this week
Write the number on a piece of paper. Say it out loud once. If you cannot say it without explaining, then practise exactly that, and not the arguments.