The issue of raising money to support operating costs and staffing has always been challenging for NGOs. If you are applying for funding to a grant-maker, it is important to not under-estimate the hidden costs which should also be included in the budget.
For example, rent, rates, IT, utilities, support staff etc. For staff whose salary is to be supported by the grant, then it would be expected that you consider a level of effort for certain roles and budget for these.
This video will suggest you the best way to raise unrestricted income for staff and overheads. Good luck!