Instead of preparing a 12-month budget for your company all at once, do a “post mortem” at the end of each month while everything is fresh in your mind.
Ask yourself, “If I had to do last month over again, what would I do differently next year?” Determine next year’s monthly budget for your income statement for each revenue and expense line.
If you have assigned profit and loss line responsibilities to your management team for their areas of responsibility, ask them to set their next year budget for their area for that month. Compare their monthly budget with yours and either accept their budget or challenge them to improve their numbers. 
Budgeting your accounts every month-end will allow you to produce a rolling 13-month budget—enabling you to both save time when working on your annual budget and produce a more accurate budget.
This process will result in a win/win situation. The more accurate budgets result in a constant annual budget and ownership of the budget by your management team.

Cameron Inglis, Germinate Inc., Winnipeg, MB