Expect a response from funding agencies in a timely manner. Most funding agencies will inform applicants of the date by which a decision will be made on an application. Remember that the reason for rejection may not be due to obvious flaws in the proposal but may just be that the application was not competitive, compared to others considered by the funding committee.
Remember that a successful application is only the start. Funders are interested in the progress of the project. They should be informed of any major findings, especially if there are going to be publications or if the results are controversial or groundbreaking. Funders may wish to publicize these, and they often have the resources to do so effectively.
Funding agency staff are usually prepared to offer advice on grant issues, and keeping them informed of important developments in a timely manner is advisable, for ex- ample, unavoidable delays to a study, changes to the study design, extension requests, etc. If delays are anticipated, it is much better to notify the agency early, so they are not wrong-footed but can work with you to mitigate the impact of these delays. For ex- ample, given sufficient notice, they may be able to revise the trial budget to allow money to be spent later than was originally agreed.