I've spent nearly a decade writing, reviewing, and managing everything about the grant making process, and I can certainly write about the common mistakes I find. Most are minor. Some can be big and cost the organization lots of points, or even get it disqualified.
So, to my grant writing friends and non-profit colleagues, here are some very important tips when putting your grant proposal together:
Don't turn it in late, or think someone will be nice and accept it anyway. Read the notice carefully. When it reads "due in the office by close of business, 5:00 p.m. Eastern Time, Thursday, January 27" you better damn make sure it comes right in time. That doesn't translate into your application being postmarked on that date, so make sure you get it to your courier on time. I once turned away a young girl (she had to have been 18) who drove up from Lakeland to Tallahassee and arrived at our office at 5:15 p.m. Her mother called me at 4:50 p.m. saying her daughter was just off I-10 and coming to the office. I warned her that the doors are locked at 5:00. The doors were locked on time, and the girl was pounding the door asking us to open. I warned my colleagues leaving the building not to accept the application if she approached them. No doubt these would-be applicants learned their lesson, but it certainly wouldn't be fair to the 100+ other applicants who turned their proposals on time.
Don't even dare to recycle support letters, or worse, use generic form letters. I have reviewed proposals where you can line up the support letters and flip through and read them line by line. I have also read support letters intended for another grant. First, it demonstrates the applicant takes the easy way out by typing some generic letter and asking its partners or potential partners to paste it onto letterhead, sign it and return it. (My experience has taught me the slacker grant applicant is most likely to become the slacker grant reporter.) Second, it demonstrates the partnership is rather shallow and superficial. A great letter of support should be a letter of COMMITMENT, demonstrating what the partner will provide in support of the applicant should it be awarded the grant. This commitment may include technical assistance, training, or match (in-kind or cash).
Don't ever use Wikipedia as a source. That's my big pet peeve! It's not reliable and again demonstrates another easy way out. A well-trained grant writer should already have good statistics and data already in his or her portfolio. Warning! Use those stats and data sparingly in your proposal, to drive home the statement of need. It's a grant proposal, not a resurrection of U.S. Census data.
Don't ever ignore a grant checklist. My technical review--the review I conduct when an application first arrives in the office-- is where many proposals are killed before they're ever read. That technical review is the exact checklist that I include in the Notice of Funding Availability (or Request for Funding Proposals). If that checklist includes a copy of the IRS Determination Letter for 501c(3) status for your organization, you better well include that! The same goes for an authorized board member signature, or a copy of the organization's last audit. Don't ever think you can be sneaky and find some "substitute." I've been blessed on the phone for killing a proposal because someone thought it would be cute to put its annual report filled with pics of cute kids in place of its last audit.
Don't ever think sneaking in an extra page is okay when there's a page limit. Remember that checklist? On my checklist, I often include details that proposals should be a certain amount of pages AND have one inch margins and 12 pt. font. Yes, I kept a ruler handy and would compare fonts if necessary. Reviewers have a large amount to read, and yes, those extra pages can add up.
Don't just run your application through the copier feeder and think you're done. Check your copies, and check them again! A funder may require that you submit an original application and additional copies. Those copies may be kept by different departments of the funder, or sent out to reviewers. When an application arrives and I perform the technical review, it is exclusively done on the original. I usually verify that the correct number of copies are there. The copies are sent to reviewers, who are free to mark and make notes on them. I can recall a few instances when reviewers would e-mail me questions because their copies were incomplete or missing information. I always advise my reviewers their scores should reflect on what information was provided, so if anything was missing, the applicant's score would be very low.
The best advice I can offer a grant writer, though, is to really get to know your potential funders. People would stalk me at conferences and meetings seeking assistance or inside information about grant funding. It never bothered me, though, and I would offer as much help as I could as long as there wasn't an open competitive application at the time. I always feel if I could offer great technical assistance up front, I'd eventually end up with some really great proposals.
There are many more other tips I can provide, but I'll just leave it at that for now. Some think grant writing is easy money, but it's very competitive. In some ways, it can be thrilling (only a nerd like me would think that, of course). Best of luck!