Budget restrictions: Look in the grant announcement to see if there are special budget restrictions or requirements (i.e. maximum budget allowed, salary cap, salary charge limit for key personnel, allowed or un-allowed costs, indirect costs treatment, etc).
Personnel: Start listing the personnel (key and non-key) and determine the level of effort commitment for each of them to carry out the work involved in the proposed project (as a percentage of their FTE). The salary charges as a percentage of their current base salaries should match the percent effort commitment (unless there is a requirement for effort cost-sharing). Fringe benefits are in addition to the base salary.
Other expenses: List all other expenses associated with the proposed work: animal purchase, animal maintenance, lab supplies and consumables, core facilities fees, travel, publication costs, subjects compensation, promotional materials, tuition costs, subcontractors' costs, etc. Add everything up to determine the total direct budget. In most cases, the indirect costs (or "Facilities and Administration" or overhead) are calculated as a percentage of the direct costs and then added to the direct budget to determine the total budget. Be aware that sometimes the indirect costs are included in the total budget limit.