Because it will be read by virtually everyone who reads the proposal, the Executive Summary should be concise, readable and avoid technical jargon. Bear in mind that the readers are likely to be impatient and lacking in technical training, if not extremely stressed.
That being the case, bid writers should focus on the win themes that are the focus throughout the tender. Keep it short and relevant. Resist the urge to simply summarise everything else in the tender proposal: you should already have a table of contents.
Finally, it is worth bid writers taking extra time to ensure that your executive summary is properly presented. It is vital to proof read it carefully, given its importance to the success of the tender proposal.