A special assessment is the most contested thing most boards ever do. Almost all of the damage is done before the vote.
Show the work that led here
Owners accept a large number far more readily when they can see the chain: the study said this component was due, the reserve reached this balance, the quotes came in at this figure, and the gap is this.
A number presented without that chain reads as a decision that was taken somewhere else and announced.
Present the alternatives honestly, including the ones you rejected
There are usually four: assess in full, assess by instalment, borrow, or defer the work. Each has a real cost, and deferring has the largest one hidden in it.
Boards that present only their preferred option invite the meeting to invent the others. Boards that price all four control the conversation.
Let owners choose how to pay where you can
The same total can be paid in full by an owner with cash and financed by an owner without. A structure that offers both means the assessment is not a forced sale for anybody, and it removes the single most emotive argument against it.
Notice earlier than the statute requires
The statutory notice period is the minimum. The useful period is longer, because an owner who first hears about a large levy on the notice is answering emotionally, and an owner who has been reading about it for a while is answering financially.
Never dress it up
Do not describe a levy as an investment or a special opportunity. Owners know what it is. Plain description costs nothing and every softened word spent here is spent against the board's credibility for the next one.
Publish what it bought
When the work is done, publish the final cost against the assessment and what happened to any surplus. The next assessment will be easier because of it.