Fellowship schemes
A common mistake is not starting to develop your proposal early enough. You want your proposal to be the best it can be and internal and external review as well as costing agreements etc. take time.
As a guide, if you have an idea and are ready to dedicate yourself to writing, you would still want a minimum of 3-6 months to put a proposal together, allowing an additional month for peer-review and revisions. Some schemes also have an internal demand management process, which will extend this period of development further.