1. Tell how many users you need for the system. If there are different groups of users such as internal and external reviewers, or occasional users, try to differentiate among them. The number of users make a big difference in the price of software licenses.
2. Tell us your budget. I know this seems impossible, but it would save a great deal of time for the buyer and the seller. Buyers have budgets set before they send out solicitations, and some proposals are rejected because they are outside the budgeted amount. Even bids that are too low may be rejected as unrealistic.
3. Be specific about requirements. Tell us the details of your particular process and especially what you think makes it unique. Include samples of forms and documents that you use, or the manual for the system you are planning to replace. Describe your processes and workflows step-by-step in plain English, either as use cases or in another format.
4. Describe your environment and your hardware and software standards. How strong are these preferences?
Now for some items that you should not include in an RFP:
1. Platitudes are not requirements. If I had a nickel for every time I saw "user friendly" or "completely integrated"... These are meaningless expressions that don't help you get a better system in the end.
2. Unless you have already chosen a vendor and the bid process is a formality, don't ask vendors to claim they have done exactly what you want with a customer exactly like you. This may eliminate some innovative proposals that might save you time and money.
3. Don't ask for open-ended integration. I have seen several RFPs which ask for integration to other systems which are not even named (or the dreaded "etc."). Integration costs cannot be estimated without detailed information on the systems to be integrated and a definition of how that integration will work.
I have seen several strong RFPs recently which included significant detail and seem likely to result in successful projects. Perhaps the tide is turning and quality will continue to improve.