Most of us have at least heard of the Seven Deadly Sins -- pride, envy, gluttony, lust, anger, greed, and sloth. There are also sins related to proposal preparation and submittal, and committing those weakens your proposal and reduces your opportunity to compete well, much less win:

1. Vagueness -- If you use a statement such as "we have one of the lowest employee turnover rates in our industry" without following that statement with the documented turnover rates for your industry and the documented turnover rates of your company, you're being vague. If you write or say something such as "we implement proven time-saving methods" without specifying what those methods are or providing examples of the methods you have implemented on similar projects, you're being vague. Anyone can make a claim -- it's facts and details that catch an evaluator's eyes.
2. Fluff -- Similar to vagueness is the sin of fluff - phrases such as "Mr. Franks is the best candidate for the key position." Is he, really? Unless you have interviewed every single eligible person worldwide who could possibly fulfill the position, it is a meaningless statement, as "best" means there is none better who is equally or similarly qualified. And should Mr. Franks ever be unavailable to fulfill the position, are you going to suggest that your customer settle for second best? A more useful and truthful statement would be based on fact, not fluff, such as, "Mr. Franks brings over 20 years of experience in managing projects equal to or larger than the proposed project. He is a certified Civil Engineer." Leave the fluff on Madison Avenue with the PR and advertising executives - provide your proposal team with bona fide facts to include in the proposal.
3. Framelessness -- The requirements set forth in the proposal instructions and evaluation factors represent the framework of the proposal. Instructions generally specify not only the content - the items/data that the evaluators consider most relevant to them for the particular procurement - but also the order in which the items are to be presented. Instructions may also include such specifics as formatting requirements (margins, font size, font type, line spacing), page limits, specifying double- or single-sided printing, requiring submittal on recycled paper, et al. Ignore these at your peril. Submitting a proposal with a framework other than that specified by the evaluators risks insulting them and having your proposal withdrawn from evaluation/competition due to non-compliance.
4. Bluster -- Such statements as "We are your best choice" or "You should select us because…" not only have the aura of Madison Avenue hard-sell fluff, but also border on the verge of bullying. Don't tell the evaluators what they should do - provide your proposal team with the data and details they have requested to show and prove to them that you are the best choice for the project.
5. Blindness - Do you turn a blind eye to any potential problems or challenges inherent in the performance of the project? There are potential and actual challenges, limitations, restrictions, and frustrations associated with various aspects of every project, both for the customer agency and the contractor. Identifying and listing those challenges - along with their potential solutions - reflects an in-depth understanding of and appreciation for the services required and your customer agency. If there is not enough data available in the solicitation and in your research of the solicitation and customer agency for you to be able to provide specific solutions, then reference - in detail - solutions to similar challenges you have implemented successfully at similar projects. Recognizing the challenges inherent in a project, along with potential solutions, enables your proposal team to lay a coherent, relevant theme to the proposal framework.
6. Denial -- Do you deny that your company has ever faced any challenges? Be honest and touch on such experiences where appropriate in the proposal and most definitely when asked for specifically. The evaluators won't believe that you've never faced any performance challenges. Present them honestly, but include the lessons learned and measures implemented to prevent recurrences of any problems, as well as methods to address future challenges proactively.
7. Omission -- Prior to submitting your proposal, be it an electronic submittal, a hard copy submittal, or both, check and double-check all relevant submittal requirements for each element of the proposal. For example, verify that all pages in each copy of each volume are present and numbered uniquely. Make sure the unit prices in your price proposal are accurate - if there is an error in your calculations, the customer agency will most likely defer to the unit price as the accurate one. Make sure that every requirement for each volume has been addressed. Using our Proposal Checklist Before Submitting as a basis, add in any and all submittal and formatting requirements for the specific proposal and double-check them all prior to submitting your proposal.

Recognizing and striving to avoid these seven deadly proposal sins will enable you and your proposal team to prepare and submit more comprehensive, competitive proposals.